Make use of sched_yield optional in runtime

[tlwilmar]

Summary

This patch cleans up the yielding code and makes it optional. An environment variable, KMP_USE_YIELD, was added. Yielding is still on by default (KMP_USE_YIELD=1), but can be turned off completely (KMP_USE_YIELD=0), or turned on only when oversubscription is detected (KMP_USE_YIELD=2). Note that oversubscription cannot always be detected by the runtime (for example, when the runtime is initialized and the process forks, oversubscription cannot be detected currently over multiple instances of the runtime).

Because yielding can be controlled by user now, the library mode settings (from KMP_LIBRARY) for throughput and turnaround have been adjusted by altering blocktime, unless that was also explicitly set.

In the original code, there were a number of places where a double yield might have been done under oversubscription. This version checks oversubscription and if that's not going to yield, then it does the spin check.

[tlwilmar]

*ping*

[jlpeyton]

LGTM

openmp/runtime/src/dllexports

%ifndef stub
 
     #
     # The following entry points are added so that the backtraces from
     # the tools contain meaningful names for all the functions that might
     # appear in a backtrace of a thread which is blocked in the RTL.
     #
 
     # Regular entry points
-        __kmp_wait_yield_4
+        __kmp_wait_4
         __kmp_fork_call
         __kmp_invoke_microtask
     %ifdef KMP_USE_MONITOR
         __kmp_launch_monitor
         __kmp_reap_monitor
     %endif
         __kmp_launch_worker
         __kmp_reap_worker

openmp/runtime/src/exports_so.txt

 #if KMP_USE_MONITOR
         __kmp_launch_monitor;
         __kmp_reap_monitor;
 #endif
         __kmp_launch_worker;
         __kmp_reap_worker;
         __kmp_release_64;
         __kmp_wait_64;
-        __kmp_wait_yield_4;
+        __kmp_wait_4;
 
         # ittnotify symbols to be used by debugger
         __kmp_itt_fini_ittlib;
         __kmp_itt_init_ittlib;
 #endif /* USE_ITT_BUILD */
 
     local: # Non-exported symbols.
 

openmp/runtime/src/kmp.h

 // System time is retrieved sporadically while blocking.
 extern kmp_uint64 __kmp_now_nsec();
 #define KMP_NOW() __kmp_now_nsec()
 #define KMP_NOW_MSEC() (KMP_NOW() / KMP_USEC_PER_SEC)
 #define KMP_BLOCKTIME_INTERVAL(team, tid)                                      \
   (KMP_BLOCKTIME(team, tid) * KMP_USEC_PER_SEC)
 #define KMP_BLOCKING(goal, count) ((count) % 1000 != 0 || (goal) > KMP_NOW())
 #endif
-#define KMP_YIELD_NOW()                                                        \
-  (KMP_NOW_MSEC() / KMP_MAX(__kmp_dflt_blocktime, 1) %                         \
-       (__kmp_yield_on_count + __kmp_yield_off_count) <                        \
-   (kmp_uint32)__kmp_yield_on_count)
 #endif // KMP_USE_MONITOR
 
 #define KMP_MIN_STATSCOLS 40
 #define KMP_MAX_STATSCOLS 4096
 #define KMP_DEFAULT_STATSCOLS 80
 
 #define KMP_MIN_INTERVAL 0
 #define KMP_MAX_INTERVAL (INT_MAX - 1)
 #define KMP_DEFAULT_INTERVAL 0
 
 #define KMP_MIN_CHUNK 1
 #define KMP_MAX_CHUNK (INT_MAX - 1)
 #define KMP_DEFAULT_CHUNK 1
 
-#define KMP_MIN_INIT_WAIT 1
-#define KMP_MAX_INIT_WAIT (INT_MAX / 2)
-#define KMP_DEFAULT_INIT_WAIT 2048U
-
-#define KMP_MIN_NEXT_WAIT 1
-#define KMP_MAX_NEXT_WAIT (INT_MAX / 2)
-#define KMP_DEFAULT_NEXT_WAIT 1024U
-
 #define KMP_DFLT_DISP_NUM_BUFF 7
 #define KMP_MAX_ORDERED 8
 
 #define KMP_MAX_FIELDS 32
 
 #define KMP_MAX_BRANCH_BITS 31
 
 #define KMP_MAX_ACTIVE_LEVELS_LIMIT INT_MAX
typedef struct kmp_cpuid {
   kmp_uint32 ecx;
   kmp_uint32 edx;
 } kmp_cpuid_t;
 extern void __kmp_x86_cpuid(int mode, int mode2, struct kmp_cpuid *p);
 #if KMP_ARCH_X86
 extern void __kmp_x86_pause(void);
 #elif KMP_MIC
 // Performance testing on KNC (C0QS-7120 P/A/X/D, 61-core, 16 GB Memory) showed
-// regression after removal of extra PAUSE from KMP_YIELD_SPIN(). Changing
+// regression after removal of extra PAUSE from spin loops. Changing
 // the delay from 100 to 300 showed even better performance than double PAUSE
 // on Spec OMP2001 and LCPC tasking tests, no regressions on EPCC.
 static inline void __kmp_x86_pause(void) { _mm_delay_32(300); }
 #else
 static inline void __kmp_x86_pause(void) { _mm_pause(); }
 #endif
 #define KMP_CPU_PAUSE() __kmp_x86_pause()
 #elif KMP_ARCH_PPC64
 #define KMP_PPC64_PRI_LOW() __asm__ volatile("or 1, 1, 1")
 #define KMP_PPC64_PRI_MED() __asm__ volatile("or 2, 2, 2")
 #define KMP_PPC64_PRI_LOC_MB() __asm__ volatile("" : : : "memory")
 #define KMP_CPU_PAUSE()                                                        \
   do {                                                                         \
     KMP_PPC64_PRI_LOW();                                                       \
     KMP_PPC64_PRI_MED();                                                       \
     KMP_PPC64_PRI_LOC_MB();                                                    \
   } while (0)
 #else
 #define KMP_CPU_PAUSE() /* nothing to do */
 #endif
 
 #define KMP_INIT_YIELD(count)                                                  \
   { (count) = __kmp_yield_init; }
 
+#define KMP_OVERSUBSCRIBED                                                     \
+  (TCR_4(__kmp_nth) > (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc))
+
+#define KMP_TRY_YIELD                                                          \
+  ((__kmp_use_yield == 1) || (__kmp_use_yield == 2 && (KMP_OVERSUBSCRIBED)))
+
+#define KMP_TRY_YIELD_OVERSUB                                                  \
+  ((__kmp_use_yield == 1 || __kmp_use_yield == 2) && (KMP_OVERSUBSCRIBED))
+
 #define KMP_YIELD(cond)                                                        \
   {                                                                            \
     KMP_CPU_PAUSE();                                                           \
-    __kmp_yield((cond));                                                       \
+    if ((cond) && (KMP_TRY_YIELD))                                             \
+      __kmp_yield();                                                           \
+  }
+
+#define KMP_YIELD_OVERSUB()                                                    \
+  {                                                                            \
+    KMP_CPU_PAUSE();                                                           \
+    if ((KMP_TRY_YIELD_OVERSUB))                                               \
+      __kmp_yield();                                                           \
   }
 
 // Note the decrement of 2 in the following Macros. With KMP_LIBRARY=turnaround,
 // there should be no yielding since initial value from KMP_INIT_YIELD() is odd.
-
-#define KMP_YIELD_WHEN(cond, count)                                            \
+#define KMP_YIELD_SPIN(count)                                                  \
   {                                                                            \
     KMP_CPU_PAUSE();                                                           \
-    (count) -= 2;                                                              \
-    if (!(count)) {                                                            \
-      __kmp_yield(cond);                                                       \
-      (count) = __kmp_yield_next;                                              \
-    }                                                                          \
+    if (KMP_TRY_YIELD) {                                                       \
+      (count) -= 2;                                                            \
+      if (!(count)) {                                                          \
+        __kmp_yield();                                                         \
+        (count) = __kmp_yield_next;                                            \
+      }                                                                        \
+    }                                                                          \
   }
-#define KMP_YIELD_SPIN(count)                                                  \
+
+#define KMP_YIELD_OVERSUB_ELSE_SPIN(count)                                     \
   {                                                                            \
     KMP_CPU_PAUSE();                                                           \
-    (count) -= 2;                                                              \
-    if (!(count)) {                                                            \
-      __kmp_yield(1);                                                          \
-      (count) = __kmp_yield_next;                                              \
-    }                                                                          \
+    if ((KMP_TRY_YIELD_OVERSUB))                                               \
+      __kmp_yield();                                                           \
+    else if (__kmp_use_yield == 1) {                                           \
+      (count) -= 2;                                                            \
+      if (!(count)) {                                                          \
+        __kmp_yield();                                                         \
+        (count) = __kmp_yield_next;                                            \
+      }                                                                        \
+    }                                                                          \
   }
 
 /* ------------------------------------------------------------------------ */
 /* Support datatypes for the orphaned construct nesting checks.             */
 /* ------------------------------------------------------------------------ */
 
 enum cons_type {
   ct_none,

 extern kmp_bootstrap_lock_t
     __kmp_tp_cached_lock; /* used for the hack to allow threadprivate cache and
                              __kmp_threads expansion to co-exist */
 
 extern kmp_lock_t __kmp_global_lock; /* control OS/global access  */
 extern kmp_queuing_lock_t __kmp_dispatch_lock; /* control dispatch access  */
 extern kmp_lock_t __kmp_debug_lock; /* control I/O access for KMP_DEBUG */
 
-/* used for yielding spin-waits */
-extern unsigned int __kmp_init_wait; /* initial number of spin-tests   */
-extern unsigned int __kmp_next_wait; /* susequent number of spin-tests */
-
 extern enum library_type __kmp_library;
 
 extern enum sched_type __kmp_sched; /* default runtime scheduling */
 extern enum sched_type __kmp_static; /* default static scheduling method */
 extern enum sched_type __kmp_guided; /* default guided scheduling method */
 extern enum sched_type __kmp_auto; /* default auto scheduling method */
 extern int __kmp_chunk; /* default runtime chunk size */
 

 extern int __kmp_env_consistency_check; // was KMP_CONSISTENCY_CHECK specified?
 extern int __kmp_generate_warnings; /* should we issue warnings? */
 extern int __kmp_reserve_warn; /* have we issued reserve_threads warning? */
 
 #ifdef DEBUG_SUSPEND
 extern int __kmp_suspend_count; /* count inside __kmp_suspend_template() */
 #endif
 
+extern kmp_int32 __kmp_use_yield;
+extern kmp_int32 __kmp_use_yield_exp_set;
 extern kmp_uint32 __kmp_yield_init;
 extern kmp_uint32 __kmp_yield_next;
 
-#if KMP_USE_MONITOR
-extern kmp_uint32 __kmp_yielding_on;
-#endif
-extern kmp_uint32 __kmp_yield_cycle;
-extern kmp_int32 __kmp_yield_on_count;
-extern kmp_int32 __kmp_yield_off_count;
-
 /* ------------------------------------------------------------------------- */
 extern int __kmp_allThreadsSpecified;
 
 extern size_t __kmp_align_alloc;
 /* following data protected by initialization routines */
 extern int __kmp_xproc; /* number of processors in the system */
 extern int __kmp_avail_proc; /* number of processors available to the process */
 extern size_t __kmp_sys_min_stksize; /* system-defined minimum stack size */

 
 #if OMP_40_ENABLED
 extern void __kmp_push_proc_bind(ident_t *loc, int gtid,
                                  kmp_proc_bind_t proc_bind);
 extern void __kmp_push_num_teams(ident_t *loc, int gtid, int num_teams,
                                  int num_threads);
 #endif
 
-extern void __kmp_yield(int cond);
+extern void __kmp_yield();
 
 extern void __kmpc_dispatch_init_4(ident_t *loc, kmp_int32 gtid,
                                    enum sched_type schedule, kmp_int32 lb,
                                    kmp_int32 ub, kmp_int32 st, kmp_int32 chunk);
 extern void __kmpc_dispatch_init_4u(ident_t *loc, kmp_int32 gtid,
                                     enum sched_type schedule, kmp_uint32 lb,
                                     kmp_uint32 ub, kmp_int32 st,
                                     kmp_int32 chunk);

 
 #endif /* KMP_GOMP_COMPAT */
 
 extern kmp_uint32 __kmp_eq_4(kmp_uint32 value, kmp_uint32 checker);
 extern kmp_uint32 __kmp_neq_4(kmp_uint32 value, kmp_uint32 checker);
 extern kmp_uint32 __kmp_lt_4(kmp_uint32 value, kmp_uint32 checker);
 extern kmp_uint32 __kmp_ge_4(kmp_uint32 value, kmp_uint32 checker);
 extern kmp_uint32 __kmp_le_4(kmp_uint32 value, kmp_uint32 checker);
-extern kmp_uint32 __kmp_wait_yield_4(kmp_uint32 volatile *spinner,
-                                     kmp_uint32 checker,
-                                     kmp_uint32 (*pred)(kmp_uint32, kmp_uint32),
-                                     void *obj);
-extern void __kmp_wait_yield_4_ptr(void *spinner, kmp_uint32 checker,
-                                   kmp_uint32 (*pred)(void *, kmp_uint32),
-                                   void *obj);
+extern kmp_uint32 __kmp_wait_4(kmp_uint32 volatile *spinner, kmp_uint32 checker,
+extern void __kmp_wait_4_ptr(void *spinner, kmp_uint32 checker,
+                             kmp_uint32 (*pred)(void *, kmp_uint32), void *obj);
 
 class kmp_flag_32;
 class kmp_flag_64;
 class kmp_flag_oncore;
 extern void __kmp_wait_64(kmp_info_t *this_thr, kmp_flag_64 *flag,
                           int final_spin
 #if USE_ITT_BUILD
                           ,

openmp/runtime/src/kmp_csupport.cpp

#if KMP_OS_CNK
   // The flushing thread needs to yield here; this prevents a
   // busy-waiting thread from saturating the pipeline. flush is
   // often used in loops like this:
   // while (!flag) {
   //   #pragma omp flush(flag)
   // }
   // and adding the yield here is good for at least a 10x speedup
   // when running >2 threads per core (on the NAS LU benchmark).
-  __kmp_yield(TRUE);
+  __kmp_yield();
 #endif
 #else
 #error Unknown or unsupported architecture
 #endif
 
 #if OMPT_SUPPORT && OMPT_OPTIONAL
   if (ompt_enabled.ompt_callback_flush) {
     ompt_callbacks.ompt_callback(ompt_callback_flush)(
#define KMP_ACQUIRE_TAS_LOCK(lock, gtid)                                       \
     kmp_tas_lock_t *l = (kmp_tas_lock_t *)lock;                                \
     kmp_int32 tas_free = KMP_LOCK_FREE(tas);                                   \
     kmp_int32 tas_busy = KMP_LOCK_BUSY(gtid + 1, tas);                         \
     if (KMP_ATOMIC_LD_RLX(&l->lk.poll) != tas_free ||                          \
         !__kmp_atomic_compare_store_acq(&l->lk.poll, tas_free, tas_busy)) {    \
       kmp_uint32 spins;                                                        \
       KMP_FSYNC_PREPARE(l);                                                    \
       KMP_INIT_YIELD(spins);                                                   \
-      if (TCR_4(__kmp_nth) >                                                   \
-          (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {               \
-        KMP_YIELD(TRUE);                                                       \
-      } else {                                                                 \
-        KMP_YIELD_SPIN(spins);                                                 \
-      }                                                                        \
       kmp_backoff_t backoff = __kmp_spin_backoff_params;                       \
-      while (                                                                  \
-          KMP_ATOMIC_LD_RLX(&l->lk.poll) != tas_free ||                        \
-          !__kmp_atomic_compare_store_acq(&l->lk.poll, tas_free, tas_busy)) {  \
-        __kmp_spin_backoff(&backoff);                                          \
+      do {                                                                     \
         if (TCR_4(__kmp_nth) >                                                 \
             (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {             \
           KMP_YIELD(TRUE);                                                     \
         } else {                                                               \
           KMP_YIELD_SPIN(spins);                                               \
         }                                                                      \
-      }                                                                        \
+        __kmp_spin_backoff(&backoff);                                          \
+      } while (                                                                \
+          KMP_ATOMIC_LD_RLX(&l->lk.poll) != tas_free ||                        \
+          !__kmp_atomic_compare_store_acq(&l->lk.poll, tas_free, tas_busy));   \
     }                                                                          \
     KMP_FSYNC_ACQUIRED(l);                                                     \
   }
 
 // Fast-path test tas lock
 #define KMP_TEST_TAS_LOCK(lock, gtid, rc)                                      \
   {                                                                            \
     kmp_tas_lock_t *l = (kmp_tas_lock_t *)lock;                                \
#define KMP_RELEASE_FUTEX_LOCK(lock, gtid)                                     \
     KMP_FSYNC_RELEASING(ftx);                                                  \
     kmp_int32 poll_val =                                                       \
         KMP_XCHG_FIXED32(&(ftx->lk.poll), KMP_LOCK_FREE(futex));               \
     if (KMP_LOCK_STRIP(poll_val) & 1) {                                        \
       syscall(__NR_futex, &(ftx->lk.poll), FUTEX_WAKE,                         \
               KMP_LOCK_BUSY(1, futex), NULL, NULL, 0);                         \
     }                                                                          \
     KMP_MB();                                                                  \
-    KMP_YIELD(TCR_4(__kmp_nth) >                                               \
-              (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc));            \
+    KMP_YIELD_OVERSUB();                                                       \
   }
 
 #endif // KMP_USE_FUTEX
 
 #else // KMP_USE_DYNAMIC_LOCK
 
 static kmp_user_lock_p __kmp_get_critical_section_ptr(kmp_critical_name *crit,
                                                       ident_t const *loc,
for (j = 1; j < num_dims; ++j) {
     trace_count *= pr_buf->th_doacross_info[4 * j + 1]; // use kept ranges
   }
   KMP_DEBUG_ASSERT(trace_count > 0);
 
   // Check if shared buffer is not occupied by other loop (idx -
   // __kmp_dispatch_num_buffers)
   if (idx != sh_buf->doacross_buf_idx) {
     // Shared buffer is occupied, wait for it to be free
-    __kmp_wait_yield_4((volatile kmp_uint32 *)&sh_buf->doacross_buf_idx, idx,
-                       __kmp_eq_4, NULL);
+    __kmp_wait_4((volatile kmp_uint32 *)&sh_buf->doacross_buf_idx, idx,
   }
 #if KMP_32_BIT_ARCH
   // Check if we are the first thread. After the CAS the first thread gets 0,
   // others get 1 if initialization is in progress, allocated pointer otherwise.
   // Treat pointer as volatile integer (value 0 or 1) until memory is allocated.
   flags = (kmp_uint32 *)KMP_COMPARE_AND_STORE_RET32(
       (volatile kmp_int32 *)&sh_buf->doacross_flags, NULL, 1);
 #else

openmp/runtime/src/kmp_dispatch.h

 template <typename T> kmp_uint32 __kmp_ge(T value, T checker) {
   return value >= checker;
 }
 template <typename T> kmp_uint32 __kmp_eq(T value, T checker) {
   return value == checker;
 }
 
 /*
-    Spin wait loop that first does pause, then yield.
+    Spin wait loop that pauses between checks.
     Waits until function returns non-zero when called with *spinner and check.
     Does NOT put threads to sleep.
     Arguments:
         UT is unsigned 4- or 8-byte type
         spinner - memory location to check value
         checker - value which spinner is >, <, ==, etc.
         pred - predicate function to perform binary comparison of some sort
 #if USE_ITT_BUILD
         obj -- is higher-level synchronization object to report to ittnotify. It
         is used to report locks consistently. For example, if lock is acquired
         immediately, its address is reported to ittnotify via
         KMP_FSYNC_ACQUIRED(). However, it lock cannot be acquired immediately
-        and lock routine calls to KMP_WAIT_YIELD(), the later should report the
+        and lock routine calls to KMP_WAIT(), the later should report the
         same address, not an address of low-level spinner.
 #endif // USE_ITT_BUILD
     TODO: make inline function (move to header file for icl)
 */
 template <typename UT>
-static UT __kmp_wait_yield(volatile UT *spinner, UT checker,
-                           kmp_uint32 (*pred)(UT, UT)
-                               USE_ITT_BUILD_ARG(void *obj)) {
+static UT __kmp_wait(volatile UT *spinner, UT checker,
+                     kmp_uint32 (*pred)(UT, UT) USE_ITT_BUILD_ARG(void *obj)) {
   // note: we may not belong to a team at this point
   volatile UT *spin = spinner;
   UT check = checker;
   kmp_uint32 spins;
   kmp_uint32 (*f)(UT, UT) = pred;
   UT r;
 
   KMP_FSYNC_SPIN_INIT(obj, CCAST(UT *, spin));
   KMP_INIT_YIELD(spins);
   // main wait spin loop
   while (!f(r = *spin, check)) {
     KMP_FSYNC_SPIN_PREPARE(obj);
     /* GEH - remove this since it was accidentally introduced when kmp_wait was
        split.
        It causes problems with infinite recursion because of exit lock */
     /* if ( TCR_4(__kmp_global.g.g_done) && __kmp_global.g.g_abort)
         __kmp_abort_thread(); */
-
-    // if we are oversubscribed,
-    // or have waited a bit (and KMP_LIBRARY=throughput, then yield
-    // pause is in the following code
-    KMP_YIELD(TCR_4(__kmp_nth) > __kmp_avail_proc);
-    KMP_YIELD_SPIN(spins);
+    // If oversubscribed, or have waited a bit then yield.
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
   }
   KMP_FSYNC_SPIN_ACQUIRED(obj);
   return r;
 }
 
 /* ------------------------------------------------------------------------ */
 /* ------------------------------------------------------------------------ */
 
#ifdef KMP_DEBUG
       // create format specifiers before the debug output
       buff = __kmp_str_format("__kmp_dispatch_deo: T#%%d before wait: "
                               "ordered_iter:%%%s lower:%%%s\n",
                               traits_t<UT>::spec, traits_t<UT>::spec);
       KD_TRACE(1000, (buff, gtid, sh->u.s.ordered_iteration, lower));
       __kmp_str_free(&buff);
     }
 #endif
-    __kmp_wait_yield<UT>(&sh->u.s.ordered_iteration, lower,
-                         __kmp_ge<UT> USE_ITT_BUILD_ARG(NULL));
+    __kmp_wait<UT>(&sh->u.s.ordered_iteration, lower,
     KMP_MB(); /* is this necessary? */
 #ifdef KMP_DEBUG
     {
       char *buff;
       // create format specifiers before the debug output
       buff = __kmp_str_format("__kmp_dispatch_deo: T#%%d after wait: "
                               "ordered_iter:%%%s lower:%%%s\n",
                               traits_t<UT>::spec, traits_t<UT>::spec);

openmp/runtime/src/kmp_dispatch.cpp

#endif
 
   if (active) {
     /* The name of this buffer should be my_buffer_index when it's free to use
      * it */
 
     KD_TRACE(100, ("__kmp_dispatch_init: T#%d before wait: my_buffer_index:%d "
                    "sh->buffer_index:%d\n",
                    gtid, my_buffer_index, sh->buffer_index));
-    __kmp_wait_yield<kmp_uint32>(&sh->buffer_index, my_buffer_index,
-                                 __kmp_eq<kmp_uint32> USE_ITT_BUILD_ARG(NULL));
-    // Note: KMP_WAIT_YIELD() cannot be used there: buffer index and
+    __kmp_wait<kmp_uint32>(&sh->buffer_index, my_buffer_index,
+    // Note: KMP_WAIT() cannot be used there: buffer index and
     // my_buffer_index are *always* 32-bit integers.
     KMP_MB(); /* is this necessary? */
     KD_TRACE(100, ("__kmp_dispatch_init: T#%d after wait: my_buffer_index:%d "
                    "sh->buffer_index:%d\n",
                    gtid, my_buffer_index, sh->buffer_index));
 
     th->th.th_dispatch->th_dispatch_pr_current = (dispatch_private_info_t *)pr;
     th->th.th_dispatch->th_dispatch_sh_current =
#ifdef KMP_DEBUG
         buff = __kmp_str_format("__kmp_dispatch_finish: T#%%d before wait: "
                                 "ordered_iteration:%%%s lower:%%%s\n",
                                 traits_t<UT>::spec, traits_t<UT>::spec);
         KD_TRACE(1000, (buff, gtid, sh->u.s.ordered_iteration, lower));
         __kmp_str_free(&buff);
       }
 #endif
 
-      __kmp_wait_yield<UT>(&sh->u.s.ordered_iteration, lower,
-                           __kmp_ge<UT> USE_ITT_BUILD_ARG(NULL));
+      __kmp_wait<UT>(&sh->u.s.ordered_iteration, lower,
       KMP_MB(); /* is this necessary? */
 #ifdef KMP_DEBUG
       {
         char *buff;
         // create format specifiers before the debug output
         buff = __kmp_str_format("__kmp_dispatch_finish: T#%%d after wait: "
                                 "ordered_iteration:%%%s lower:%%%s\n",
                                 traits_t<UT>::spec, traits_t<UT>::spec);
#ifdef KMP_DEBUG
             "__kmp_dispatch_finish_chunk: T#%%d before wait: "
             "ordered_iteration:%%%s lower:%%%s upper:%%%s\n",
             traits_t<UT>::spec, traits_t<UT>::spec, traits_t<UT>::spec);
         KD_TRACE(1000, (buff, gtid, sh->u.s.ordered_iteration, lower, upper));
         __kmp_str_free(&buff);
       }
 #endif
 
-      __kmp_wait_yield<UT>(&sh->u.s.ordered_iteration, lower,
-                           __kmp_ge<UT> USE_ITT_BUILD_ARG(NULL));
+      __kmp_wait<UT>(&sh->u.s.ordered_iteration, lower,
 
       KMP_MB(); /* is this necessary? */
       KD_TRACE(1000, ("__kmp_dispatch_finish_chunk: T#%d resetting "
                       "ordered_bumped to zero\n",
                       gtid));
       pr->ordered_bumped = 0;
 //!!!!! TODO check if the inc should be unsigned, or signed???
 #ifdef KMP_DEBUG
kmp_uint32 __kmp_ge_4(kmp_uint32 value, kmp_uint32 checker) {
   return value >= checker;
 }
 
 kmp_uint32 __kmp_le_4(kmp_uint32 value, kmp_uint32 checker) {
   return value <= checker;
 }
 
 kmp_uint32
-__kmp_wait_yield_4(volatile kmp_uint32 *spinner, kmp_uint32 checker,
-                   kmp_uint32 (*pred)(kmp_uint32, kmp_uint32),
-                   void *obj // Higher-level synchronization object, or NULL.
-                   ) {
+__kmp_wait_4(volatile kmp_uint32 *spinner, kmp_uint32 checker,
   // note: we may not belong to a team at this point
   volatile kmp_uint32 *spin = spinner;
   kmp_uint32 check = checker;
   kmp_uint32 spins;
   kmp_uint32 (*f)(kmp_uint32, kmp_uint32) = pred;
   kmp_uint32 r;
 
   KMP_FSYNC_SPIN_INIT(obj, CCAST(kmp_uint32 *, spin));
   KMP_INIT_YIELD(spins);
   // main wait spin loop
   while (!f(r = TCR_4(*spin), check)) {
     KMP_FSYNC_SPIN_PREPARE(obj);
     /* GEH - remove this since it was accidentally introduced when kmp_wait was
        split. It causes problems with infinite recursion because of exit lock */
     /* if ( TCR_4(__kmp_global.g.g_done) && __kmp_global.g.g_abort)
         __kmp_abort_thread(); */
-
-    /* if we have waited a bit, or are oversubscribed, yield */
-    /* pause is in the following code */
-    KMP_YIELD(TCR_4(__kmp_nth) > __kmp_avail_proc);
-    KMP_YIELD_SPIN(spins);
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
   }
   KMP_FSYNC_SPIN_ACQUIRED(obj);
   return r;
 }
 
-void __kmp_wait_yield_4_ptr(
-    void *spinner, kmp_uint32 checker, kmp_uint32 (*pred)(void *, kmp_uint32),
+void __kmp_wait_4_ptr(void *spinner, kmp_uint32 checker,
+                      kmp_uint32 (*pred)(void *, kmp_uint32),
                       void *obj // Higher-level synchronization object, or NULL.
                       ) {
   // note: we may not belong to a team at this point
   void *spin = spinner;
   kmp_uint32 check = checker;
   kmp_uint32 spins;
   kmp_uint32 (*f)(void *, kmp_uint32) = pred;
 
   KMP_FSYNC_SPIN_INIT(obj, spin);
   KMP_INIT_YIELD(spins);
   // main wait spin loop
   while (!f(spin, check)) {
     KMP_FSYNC_SPIN_PREPARE(obj);
-    /* if we have waited a bit, or are oversubscribed, yield */
+    /* if we have waited a bit, or are noversubscribed, yield */
     /* pause is in the following code */
-    KMP_YIELD(TCR_4(__kmp_nth) > __kmp_avail_proc);
-    KMP_YIELD_SPIN(spins);
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
   }
   KMP_FSYNC_SPIN_ACQUIRED(obj);
 }
 
 } // extern "C"
 
 #ifdef KMP_GOMP_COMPAT
 

openmp/runtime/src/kmp_dispatch_hier.h

void core_barrier_impl<T>::barrier(kmp_int32 id,
   kmp_uint64 next_wait_value =
       (current_wait_value ? 0 : get_wait_val(tdata->num_active));
   KD_TRACE(10, ("core_barrier_impl::barrier(): T#%d current_index:%llu "
                 "next_index:%llu curr_wait:%llu next_wait:%llu\n",
                 __kmp_get_gtid(), current_index, next_index, current_wait_value,
                 next_wait_value));
   char v = (current_wait_value ? 0x1 : 0x0);
   (RCAST(volatile char *, &(bdata->val[current_index])))[id] = v;
-  __kmp_wait_yield<kmp_uint64>(&(bdata->val[current_index]), current_wait_value,
-                               __kmp_eq<kmp_uint64> USE_ITT_BUILD_ARG(NULL));
+  __kmp_wait<kmp_uint64>(&(bdata->val[current_index]), current_wait_value,
   tdata->wait_val[current_index] = next_wait_value;
   tdata->index = next_index;
 }
 
 // Counter barrier implementation
 // Can be used in a unit with arbitrary number of active threads
 template <typename T> class counter_barrier_impl {
 public:
void counter_barrier_impl<T>::barrier(kmp_int32 id,
   kmp_uint64 next_wait_value = current_wait_value + tdata->num_active;
 
   KD_TRACE(10, ("counter_barrier_impl::barrier(): T#%d current_index:%llu "
                 "next_index:%llu curr_wait:%llu next_wait:%llu\n",
                 __kmp_get_gtid(), current_index, next_index, current_wait_value,
                 next_wait_value));
   val = RCAST(volatile kmp_int64 *, &(bdata->val[current_index]));
   KMP_TEST_THEN_INC64(val);
-  __kmp_wait_yield<kmp_uint64>(&(bdata->val[current_index]), current_wait_value,
-                               __kmp_ge<kmp_uint64> USE_ITT_BUILD_ARG(NULL));
+  __kmp_wait<kmp_uint64>(&(bdata->val[current_index]), current_wait_value,
   tdata->wait_val[current_index] = next_wait_value;
   tdata->index = next_index;
 }
 
 // Data associated with topology unit within a layer
 // For example, one kmp_hier_top_unit_t corresponds to one L1 cache
 template <typename T> struct kmp_hier_top_unit_t {
   typedef typename traits_t<T>::signed_t ST;

openmp/runtime/src/kmp_global.cpp

 
 int __kmp_init_counter = 0;
 int __kmp_root_counter = 0;
 int __kmp_version = 0;
 
 std::atomic<kmp_int32> __kmp_team_counter = ATOMIC_VAR_INIT(0);
 std::atomic<kmp_int32> __kmp_task_counter = ATOMIC_VAR_INIT(0);
 
-unsigned int __kmp_init_wait =
-    KMP_DEFAULT_INIT_WAIT; /* initial number of spin-tests   */
-unsigned int __kmp_next_wait =
-    KMP_DEFAULT_NEXT_WAIT; /* susequent number of spin-tests */
-
 size_t __kmp_stksize = KMP_DEFAULT_STKSIZE;
 #if KMP_USE_MONITOR
 size_t __kmp_monitor_stksize = 0; // auto adjust
 #endif
 size_t __kmp_stkoffset = KMP_DEFAULT_STKOFFSET;
 int __kmp_stkpadding = KMP_MIN_STKPADDING;
 
 size_t __kmp_malloc_pool_incr = KMP_DEFAULT_MALLOC_POOL_INCR;
int __kmp_need_register_atfork =
     TRUE; /* At initialization, call pthread_atfork to install fork handler */
 int __kmp_need_register_atfork_specified = TRUE;
 
 int __kmp_env_stksize = FALSE; /* KMP_STACKSIZE specified? */
 int __kmp_env_blocktime = FALSE; /* KMP_BLOCKTIME specified? */
 int __kmp_env_checks = FALSE; /* KMP_CHECKS specified?    */
 int __kmp_env_consistency_check = FALSE; /* KMP_CONSISTENCY_CHECK specified? */
 
+// From KMP_USE_YIELD:
+// 0 = never yield;
+// 1 = always yield (default);
+// 2 = yield only if oversubscribed
+kmp_int32 __kmp_use_yield = 1;
+// This will be 1 if KMP_USE_YIELD environment variable was set explicitly
+kmp_int32 __kmp_use_yield_exp_set = 0;
+
 kmp_uint32 __kmp_yield_init = KMP_INIT_WAIT;
 kmp_uint32 __kmp_yield_next = KMP_NEXT_WAIT;
 
-#if KMP_USE_MONITOR
-kmp_uint32 __kmp_yielding_on = 1;
-#endif
-#if KMP_OS_CNK
-kmp_uint32 __kmp_yield_cycle = 0;
-#else
-kmp_uint32 __kmp_yield_cycle = 1; /* Yield-cycle is on by default */
-#endif
-kmp_int32 __kmp_yield_on_count =
-    10; /* By default, yielding is on for 10 monitor periods. */
-kmp_int32 __kmp_yield_off_count =
-    1; /* By default, yielding is off for 1 monitor periods. */
-
 /* ------------------------------------------------------ */
 /* STATE mostly syncronized with global lock */
 /* data written to rarely by masters, read often by workers */
 /* TODO: None of this global padding stuff works consistently because the order
    of declaration is not necessarily correlated to storage order. To fix this,
    all the important globals must be put in a big structure instead. */
 KMP_ALIGN_CACHE
 kmp_info_t **__kmp_threads = NULL;

openmp/runtime/src/kmp_itt.h

 #define KMP_FSYNC_CANCEL(obj) __itt_fsync_cancel((void *)(obj))
 #define KMP_FSYNC_ACQUIRED(obj) __itt_fsync_acquired((void *)(obj))
 #define KMP_FSYNC_RELEASING(obj) __itt_fsync_releasing((void *)(obj))
 
 /* In case of waiting in a spin loop, ITT wants KMP_FSYNC_PREPARE() to be called
    with a delay (and not called at all if waiting time is small). So, in spin
    loops, do not use KMP_FSYNC_PREPARE(), but use KMP_FSYNC_SPIN_INIT() (before
    spin loop), KMP_FSYNC_SPIN_PREPARE() (whithin the spin loop), and
-   KMP_FSYNC_SPIN_ACQUIRED(). See KMP_WAIT_YIELD() for example. */
+   KMP_FSYNC_SPIN_ACQUIRED(). See KMP_WAIT() for example. */
 
 #undef KMP_FSYNC_SPIN_INIT
 #define KMP_FSYNC_SPIN_INIT(obj, spin)                                         \
   int sync_iters = 0;                                                          \
   if (__itt_fsync_prepare_ptr) {                                               \
     if (obj == NULL) {                                                         \
       obj = spin;                                                              \
     } /* if */                                                                 \

openmp/runtime/src/kmp_lock.h

if (__kmp_env_consistency_check) {                                         \
         KMP_FATAL(LockIsAlreadyOwned, func);                                   \
       }                                                                        \
     }                                                                          \
     if (lck->tas.lk.poll != 0 ||                                               \
         !__kmp_atomic_compare_store_acq(&lck->tas.lk.poll, 0, gtid + 1)) {     \
       kmp_uint32 spins;                                                        \
       KMP_FSYNC_PREPARE(lck);                                                  \
       KMP_INIT_YIELD(spins);                                                   \
-      if (TCR_4(__kmp_nth) >                                                   \
-          (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {               \
-        KMP_YIELD(TRUE);                                                       \
-      } else {                                                                 \
-        KMP_YIELD_SPIN(spins);                                                 \
-      }                                                                        \
-      while (lck->tas.lk.poll != 0 || !__kmp_atomic_compare_store_acq(         \
-                                          &lck->tas.lk.poll, 0, gtid + 1)) {   \
-        if (TCR_4(__kmp_nth) >                                                 \
-            (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {             \
-          KMP_YIELD(TRUE);                                                     \
-        } else {                                                               \
-          KMP_YIELD_SPIN(spins);                                               \
-        }                                                                      \
-      }                                                                        \
+      do {                                                                     \
+        KMP_YIELD_OVERSUB_ELSE_SPIN(spins);                                    \
+      } while (                                                                \
+          lck->tas.lk.poll != 0 ||                                             \
+          !__kmp_atomic_compare_store_acq(&lck->tas.lk.poll, 0, gtid + 1));    \
     }                                                                          \
     KMP_FSYNC_ACQUIRED(lck);                                                   \
   } else {                                                                     \
     KMP_DEBUG_ASSERT(__kmp_acquire_user_lock_with_checks_ != NULL);            \
     (*__kmp_acquire_user_lock_with_checks_)(lck, gtid);                        \
   }
 
 #else
if (lck->tas.lk.poll - 1 == gtid) {                                        \
       lck->tas.lk.depth_locked += 1;                                           \
       *depth = KMP_LOCK_ACQUIRED_NEXT;                                         \
     } else {                                                                   \
       if ((lck->tas.lk.poll != 0) ||                                           \
           !__kmp_atomic_compare_store_acq(&lck->tas.lk.poll, 0, gtid + 1)) {   \
         kmp_uint32 spins;                                                      \
         KMP_FSYNC_PREPARE(lck);                                                \
         KMP_INIT_YIELD(spins);                                                 \
-        if (TCR_4(__kmp_nth) >                                                 \
-            (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {             \
-          KMP_YIELD(TRUE);                                                     \
-        } else {                                                               \
-          KMP_YIELD_SPIN(spins);                                               \
-        }                                                                      \
-        while (                                                                \
+        do {                                                                   \
+          KMP_YIELD_OVERSUB_ELSE_SPIN(spins);                                  \
+        } while (                                                              \
             (lck->tas.lk.poll != 0) ||                                         \
-            !__kmp_atomic_compare_store_acq(&lck->tas.lk.poll, 0, gtid + 1)) { \
-          if (TCR_4(__kmp_nth) >                                               \
-              (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {           \
-            KMP_YIELD(TRUE);                                                   \
-          } else {                                                             \
-            KMP_YIELD_SPIN(spins);                                             \
-          }                                                                    \
-        }                                                                      \
+            !__kmp_atomic_compare_store_acq(&lck->tas.lk.poll, 0, gtid + 1));  \
       }                                                                        \
       lck->tas.lk.depth_locked = 1;                                            \
       *depth = KMP_LOCK_ACQUIRED_FIRST;                                        \
     }                                                                          \
     KMP_FSYNC_ACQUIRED(lck);                                                   \
   } else {                                                                     \
     KMP_DEBUG_ASSERT(__kmp_acquire_nested_user_lock_with_checks_ != NULL);     \
     *depth = (*__kmp_acquire_nested_user_lock_with_checks_)(lck, gtid);        \

openmp/runtime/src/kmp_lock.cpp

if (KMP_ATOMIC_LD_RLX(&lck->lk.poll) == tas_free &&
       __kmp_atomic_compare_store_acq(&lck->lk.poll, tas_free, tas_busy)) {
     KMP_FSYNC_ACQUIRED(lck);
     return KMP_LOCK_ACQUIRED_FIRST;
   }
 
   kmp_uint32 spins;
   KMP_FSYNC_PREPARE(lck);
   KMP_INIT_YIELD(spins);
-  if (TCR_4(__kmp_nth) > (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {
-    KMP_YIELD(TRUE);
-  } else {
-    KMP_YIELD_SPIN(spins);
-  }
-
   kmp_backoff_t backoff = __kmp_spin_backoff_params;
-  while (KMP_ATOMIC_LD_RLX(&lck->lk.poll) != tas_free ||
-         !__kmp_atomic_compare_store_acq(&lck->lk.poll, tas_free, tas_busy)) {
+  do {
     __kmp_spin_backoff(&backoff);
-    if (TCR_4(__kmp_nth) >
-        (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc)) {
-      KMP_YIELD(TRUE);
-    } else {
-      KMP_YIELD_SPIN(spins);
-    }
-  }
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
+  } while (KMP_ATOMIC_LD_RLX(&lck->lk.poll) != tas_free ||
+           !__kmp_atomic_compare_store_acq(&lck->lk.poll, tas_free, tas_busy));
   KMP_FSYNC_ACQUIRED(lck);
   return KMP_LOCK_ACQUIRED_FIRST;
 }
 
 int __kmp_acquire_tas_lock(kmp_tas_lock_t *lck, kmp_int32 gtid) {
   int retval = __kmp_acquire_tas_lock_timed_template(lck, gtid);
   ANNOTATE_TAS_ACQUIRED(lck);
   return retval;

 int __kmp_release_tas_lock(kmp_tas_lock_t *lck, kmp_int32 gtid) {
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 
   KMP_FSYNC_RELEASING(lck);
   ANNOTATE_TAS_RELEASED(lck);
   KMP_ATOMIC_ST_REL(&lck->lk.poll, KMP_LOCK_FREE(tas));
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 
-  KMP_YIELD(TCR_4(__kmp_nth) >
-            (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc));
+  KMP_YIELD_OVERSUB();
   return KMP_LOCK_RELEASED;
 }
 
 static int __kmp_release_tas_lock_with_checks(kmp_tas_lock_t *lck,
                                               kmp_int32 gtid) {
   char const *const func = "omp_unset_lock";
   KMP_MB(); /* in case another processor initialized lock */
   if ((sizeof(kmp_tas_lock_t) <= OMP_LOCK_T_SIZE) &&
syscall(__NR_futex, &(lck->lk.poll), FUTEX_WAKE, KMP_LOCK_BUSY(1, futex),
             NULL, NULL, 0);
   }
 
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 
   KA_TRACE(1000, ("__kmp_release_futex_lock: lck:%p(0x%x), T#%d exiting\n", lck,
                   lck->lk.poll, gtid));
 
-  KMP_YIELD(TCR_4(__kmp_nth) >
-            (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc));
+  KMP_YIELD_OVERSUB();
   return KMP_LOCK_RELEASED;
 }
 
 static int __kmp_release_futex_lock_with_checks(kmp_futex_lock_t *lck,
                                                 kmp_int32 gtid) {
   char const *const func = "omp_unset_lock";
   KMP_MB(); /* in case another processor initialized lock */
   if ((sizeof(kmp_futex_lock_t) <= OMP_LOCK_T_SIZE) &&
if (std::atomic_load_explicit(&lck->lk.now_serving,
     __kmp_printf("LOCK CONTENTION: %p\n", lck);
 /* else __kmp_printf( "." );*/
 #endif /* USE_LOCK_PROFILE */
 
   if (std::atomic_load_explicit(&lck->lk.now_serving,
                                 std::memory_order_acquire) == my_ticket) {
     return KMP_LOCK_ACQUIRED_FIRST;
   }
-  KMP_WAIT_YIELD_PTR(&lck->lk.now_serving, my_ticket, __kmp_bakery_check, lck);
+  KMP_WAIT_PTR(&lck->lk.now_serving, my_ticket, __kmp_bakery_check, lck);
   return KMP_LOCK_ACQUIRED_FIRST;
 }
 
 int __kmp_acquire_ticket_lock(kmp_ticket_lock_t *lck, kmp_int32 gtid) {
   int retval = __kmp_acquire_ticket_lock_timed_template(lck, gtid);
   ANNOTATE_TICKET_ACQUIRED(lck);
   return retval;
 }
if (enqueued) {
         KMP_ASSERT(tail_thr != NULL);
         tail_thr->th.th_next_waiting = gtid + 1;
         /* corresponding wait for this write in release code */
       }
       KA_TRACE(1000,
                ("__kmp_acquire_queuing_lock: lck:%p, T#%d waiting for lock\n",
                 lck, gtid));
 
-      /* ToDo: May want to consider using __kmp_wait_sleep  or something that
-         sleeps for throughput only here. */
       KMP_MB();
-      KMP_WAIT_YIELD(spin_here_p, FALSE, KMP_EQ, lck);
+      // ToDo: Use __kmp_wait_sleep or similar when blocktime != inf
+      KMP_WAIT(spin_here_p, FALSE, KMP_EQ, lck);
 
 #ifdef DEBUG_QUEUING_LOCKS
       TRACE_LOCK(gtid + 1, "acq spin");
 
       if (this_thr->th.th_next_waiting != 0)
         __kmp_dump_queuing_lock(this_thr, gtid, lck, *head_id_p, *tail_id_p);
 #endif
       KMP_DEBUG_ASSERT(this_thr->th.th_next_waiting == 0);
#endif
 
       /* got lock, we were dequeued by the thread that released lock */
       return KMP_LOCK_ACQUIRED_FIRST;
     }
 
     /* Yield if number of threads > number of logical processors */
     /* ToDo: Not sure why this should only be in oversubscription case,
        maybe should be traditional YIELD_INIT/YIELD_WHEN loop */
-    KMP_YIELD(TCR_4(__kmp_nth) >
-              (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc));
+    KMP_YIELD_OVERSUB();
+
 #ifdef DEBUG_QUEUING_LOCKS
     TRACE_LOCK(gtid + 1, "acq retry");
 #endif
   }
   KMP_ASSERT2(0, "should not get here");
   return KMP_LOCK_ACQUIRED_FIRST;
 }
 
#ifdef DEBUG_QUEUING_LOCKS
           __kmp_dump_queuing_lock(this_thr, gtid, lck, head, tail);
 #endif
         KMP_DEBUG_ASSERT(head > 0 && tail > 0);
 
         /* try (h,t)->(h',t) or (t,t) */
         KMP_MB();
         /* make sure enqueuing thread has time to update next waiting thread
          * field */
-        *head_id_p = KMP_WAIT_YIELD((volatile kmp_uint32 *)waiting_id_p, 0,
-                                    KMP_NEQ, NULL);
+        *head_id_p =
+            KMP_WAIT((volatile kmp_uint32 *)waiting_id_p, 0, KMP_NEQ, NULL);
 #ifdef DEBUG_QUEUING_LOCKS
         TRACE_LOCK(gtid + 1, "rel deq: (h,t)->(h',t)");
 #endif
         dequeued = TRUE;
       }
     }
 
     if (dequeued) {
if (__kmp_should_speculate(lck, gtid)) {
     } else {
       // We can't try speculation until the lock is free, so we pause here
       // (without suspending on the queueing lock, to allow it to drain, then
       // try again. All other threads will also see the same result for
       // shouldSpeculate, so will be doing the same if they try to claim the
       // lock from now on.
       while (!__kmp_is_unlocked_queuing_lock(GET_QLK_PTR(lck))) {
         KMP_INC_STAT(lck, lemmingYields);
-        __kmp_yield(TRUE);
+        KMP_YIELD(TRUE);
       }
 
       if (__kmp_test_adaptive_lock_only(lck, gtid))
         return;
     }
   }
 
   // Speculative acquisition failed, so acquire it non-speculatively.
if (polls[ticket & mask] != ticket)
     __kmp_printf("LOCK CONTENTION: %p\n", lck);
 /* else __kmp_printf( "." );*/
 #endif /* USE_LOCK_PROFILE */
 
   // Now spin-wait, but reload the polls pointer and mask, in case the
   // polling area has been reconfigured.  Unless it is reconfigured, the
   // reloads stay in L1 cache and are cheap.
   //
-  // Keep this code in sync with KMP_WAIT_YIELD, in kmp_dispatch.cpp !!!
-  //
-  // The current implementation of KMP_WAIT_YIELD doesn't allow for mask
+  // Keep this code in sync with KMP_WAIT, in kmp_dispatch.cpp !!!
+  // The current implementation of KMP_WAIT doesn't allow for mask
   // and poll to be re-read every spin iteration.
   kmp_uint32 spins;
-
   KMP_FSYNC_PREPARE(lck);
   KMP_INIT_YIELD(spins);
   while (polls[ticket & mask] < ticket) { // atomic load
-    // If we are oversubscribed,
-    // or have waited a bit (and KMP_LIBRARY=turnaround), then yield.
-    // CPU Pause is in the macros for yield.
-    //
-    KMP_YIELD(TCR_4(__kmp_nth) >
-              (__kmp_avail_proc ? __kmp_avail_proc : __kmp_xproc));
-    KMP_YIELD_SPIN(spins);
-
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
     // Re-read the mask and the poll pointer from the lock structure.
     //
     // Make certain that "mask" is read before "polls" !!!
     //
     // If another thread picks reconfigures the polling area and updates their
     // values, and we get the new value of mask and the old polls pointer, we
     // could access memory beyond the end of the old polling area.
     mask = lck->lk.mask; // atomic load
do {
     status = _xbegin();
     if (status == _XBEGIN_STARTED) {
       if (__kmp_is_unlocked_queuing_lock(lck))
         return;
       _xabort(0xff);
     }
     if ((status & _XABORT_EXPLICIT) && _XABORT_CODE(status) == 0xff) {
       // Wait until lock becomes free
-      while (!__kmp_is_unlocked_queuing_lock(lck))
-        __kmp_yield(TRUE);
+      while (!__kmp_is_unlocked_queuing_lock(lck)) {
+        KMP_YIELD(TRUE);
+      }
     } else if (!(status & _XABORT_RETRY))
       break;
   } while (retries--);
 
   // Fall-back non-speculative lock (xchg)
   __kmp_acquire_queuing_lock(lck, gtid);
 }
 

openmp/runtime/src/kmp_os.h

 #if (CACHE_LINE < 64) && !defined(KMP_OS_DARWIN)
 // 2006-02-13: This produces too many warnings on OS X*. Disable for now
 #warning CACHE_LINE is too small.
 #endif
 #endif /* CACHE_LINE */
 
 #define KMP_CACHE_PREFETCH(ADDR) /* nothing */
 
-// Define attribute that indicates that the fall through from the previous 
+// Define attribute that indicates that the fall through from the previous
 // case label is intentional and should not be diagnosed by a compiler
 //   Code from libcxx/include/__config
 // Use a function like macro to imply that it must be followed by a semicolon
 #if __cplusplus > 201402L && __has_cpp_attribute(fallthrough)
 #  define KMP_FALLTHROUGH() [[fallthrough]]
 #elif __has_cpp_attribute(clang::fallthrough)
 #  define KMP_FALLTHROUGH() [[clang::fallthrough]]
 #elif __has_attribute(fallthough) || __GNUC__ >= 7

 typedef void (*microtask_t)(int *gtid, int *npr, ...);
 
 #ifdef USE_VOLATILE_CAST
 #define VOLATILE_CAST(x) (volatile x)
 #else
 #define VOLATILE_CAST(x) (x)
 #endif
 
-#define KMP_WAIT_YIELD __kmp_wait_yield_4
-#define KMP_WAIT_YIELD_PTR __kmp_wait_yield_4_ptr
+#define KMP_WAIT __kmp_wait_4
+#define KMP_WAIT_PTR __kmp_wait_4_ptr
 #define KMP_EQ __kmp_eq_4
 #define KMP_NEQ __kmp_neq_4
 #define KMP_LT __kmp_lt_4
 #define KMP_GE __kmp_ge_4
 #define KMP_LE __kmp_le_4
 
 /* Workaround for Intel(R) 64 code gen bug when taking address of static array
  * (Intel(R) 64 Tracker #138) */

openmp/runtime/src/kmp_runtime.cpp

 }
 
 /* ------------------------------------------------------------------------ */
 
 void __kmp_infinite_loop(void) {
   static int done = FALSE;
 
   while (!done) {
-    KMP_YIELD(1);
+    KMP_YIELD(TRUE);
   }
 }
 
 #define MAX_MESSAGE 512
 
 void __kmp_print_storage_map_gtid(int gtid, void *p1, void *p2, size_t size,
                                   char const *format, ...) {
   char buffer[MAX_MESSAGE];
BOOL WINAPI DllMain(HINSTANCE hInstDLL, DWORD fdwReason, LPVOID lpReserved) {
   }
 
   return TRUE;
 }
 
 #endif /* KMP_OS_WINDOWS */
 #endif /* KMP_DYNAMIC_LIB */
 
-/* Change the library type to "status" and return the old type */
-/* called from within initialization routines where __kmp_initz_lock is held */
-int __kmp_change_library(int status) {
-  int old_status;
-
-  old_status = __kmp_yield_init &
-               1; // check whether KMP_LIBRARY=throughput (even init count)
-
-  if (status) {
-    __kmp_yield_init |= 1; // throughput => turnaround (odd init count)
-  } else {
-    __kmp_yield_init &= ~1; // turnaround => throughput (even init count)
-  }
-
-  return old_status; // return previous setting of whether
-  // KMP_LIBRARY=throughput
-}
-
 /* __kmp_parallel_deo -- Wait until it's our turn. */
 void __kmp_parallel_deo(int *gtid_ref, int *cid_ref, ident_t *loc_ref) {
   int gtid = *gtid_ref;
 #ifdef BUILD_PARALLEL_ORDERED
   kmp_team_t *team = __kmp_team_from_gtid(gtid);
 #endif /* BUILD_PARALLEL_ORDERED */
 
   if (__kmp_env_consistency_check) {
     if (__kmp_threads[gtid]->th.th_root->r.r_active)
 #if KMP_USE_DYNAMIC_LOCK
       __kmp_push_sync(gtid, ct_ordered_in_parallel, loc_ref, NULL, 0);
 #else
       __kmp_push_sync(gtid, ct_ordered_in_parallel, loc_ref, NULL);
 #endif
   }
 #ifdef BUILD_PARALLEL_ORDERED
   if (!team->t.t_serialized) {
     KMP_MB();
-    KMP_WAIT_YIELD(&team->t.t_ordered.dt.t_value, __kmp_tid_from_gtid(gtid),
-                   KMP_EQ, NULL);
+    KMP_WAIT(&team->t.t_ordered.dt.t_value, __kmp_tid_from_gtid(gtid), KMP_EQ,
+             NULL);
     KMP_MB();
   }
 #endif /* BUILD_PARALLEL_ORDERED */
 }
 
 /* __kmp_parallel_dxo -- Signal the next task. */
 void __kmp_parallel_dxo(int *gtid_ref, int *cid_ref, ident_t *loc_ref) {
   int gtid = *gtid_ref;

 /* set the behaviour of the runtime library */
 /* TODO this can cause some odd behaviour with sibling parallelism... */
 void __kmp_aux_set_library(enum library_type arg) {
   __kmp_library = arg;
 
   switch (__kmp_library) {
   case library_serial: {
     KMP_INFORM(LibraryIsSerial);
-    (void)__kmp_change_library(TRUE);
   } break;
   case library_turnaround:
-    (void)__kmp_change_library(TRUE);
+    if (__kmp_use_yield == 1 && !__kmp_use_yield_exp_set)
+      __kmp_use_yield = 2; // only yield when oversubscribed
     break;
   case library_throughput:
-    (void)__kmp_change_library(FALSE);
+    if (__kmp_dflt_blocktime == KMP_MAX_BLOCKTIME)
+      __kmp_dflt_blocktime = 200;
     break;
   default:
     KMP_FATAL(UnknownLibraryType, arg);
   }
 }
 
 /* Getting team information common for all team API */
 // Returns NULL if not in teams construct

openmp/runtime/src/kmp_settings.cpp

 } // __kmp_stg_teams_thread_limit
 
 static void __kmp_stg_print_teams_thread_limit(kmp_str_buf_t *buffer,
                                                char const *name, void *data) {
   __kmp_stg_print_int(buffer, name, __kmp_teams_max_nth);
 } // __kmp_stg_print_teams_thread_limit
 
 // -----------------------------------------------------------------------------
+// KMP_USE_YIELD
+static void __kmp_stg_parse_use_yield(char const *name, char const *value,
+                                      void *data) {
+  __kmp_stg_parse_int(name, value, 0, 2, &__kmp_use_yield);
+  __kmp_use_yield_exp_set = 1;
+} // __kmp_stg_parse_use_yield
+
+static void __kmp_stg_print_use_yield(kmp_str_buf_t *buffer, char const *name,
+                                      void *data) {
+  __kmp_stg_print_int(buffer, name, __kmp_use_yield);
+} // __kmp_stg_print_use_yield
+
+// -----------------------------------------------------------------------------
 // KMP_BLOCKTIME
 
 static void __kmp_stg_parse_blocktime(char const *name, char const *value,
                                       void *data) {
   __kmp_dflt_blocktime = __kmp_convert_to_milliseconds(value);
   if (__kmp_dflt_blocktime < 0) {
     __kmp_dflt_blocktime = KMP_DEFAULT_BLOCKTIME;
     __kmp_msg(kmp_ms_warning, KMP_MSG(InvalidValue, name, value),
if (wait->omp) {
     } else {
       KMP_WARNING(StgInvalidValue, name, value);
     }
   } else {
     if (__kmp_str_match("serial", 1, value)) { /* S */
       __kmp_library = library_serial;
     } else if (__kmp_str_match("throughput", 2, value)) { /* TH */
       __kmp_library = library_throughput;
+      if (blocktime_str == NULL) {
+        // KMP_BLOCKTIME not specified, so set default to 0.
+        __kmp_dflt_blocktime = 0;
+      }
     } else if (__kmp_str_match("turnaround", 2, value)) { /* TU */
       __kmp_library = library_turnaround;
     } else if (__kmp_str_match("dedicated", 1, value)) { /* D */
       __kmp_library = library_turnaround;
     } else if (__kmp_str_match("multiuser", 1, value)) { /* M */
       __kmp_library = library_throughput;
+      if (blocktime_str == NULL) {
+        // KMP_BLOCKTIME not specified, so set default to 0.
+        __kmp_dflt_blocktime = 0;
+      }
     } else {
       KMP_WARNING(StgInvalidValue, name, value);
     }
   }
-  __kmp_aux_set_library(__kmp_library);
-
 } // __kmp_stg_parse_wait_policy
 
 static void __kmp_stg_print_wait_policy(kmp_str_buf_t *buffer, char const *name,
                                         void *data) {
 
   kmp_stg_wp_data_t *wait = (kmp_stg_wp_data_t *)data;
   char const *value = NULL;
 

 
 static void __kmp_stg_print_par_range_env(kmp_str_buf_t *buffer,
                                           char const *name, void *data) {
   if (__kmp_par_range != 0) {
     __kmp_stg_print_str(buffer, name, par_range_to_print);
   }
 } // __kmp_stg_print_par_range_env
 
-// -----------------------------------------------------------------------------
-// KMP_YIELD_CYCLE, KMP_YIELD_ON, KMP_YIELD_OFF
-
-static void __kmp_stg_parse_yield_cycle(char const *name, char const *value,
-                                        void *data) {
-  int flag = __kmp_yield_cycle;
-  __kmp_stg_parse_bool(name, value, &flag);
-  __kmp_yield_cycle = flag;
-} // __kmp_stg_parse_yield_cycle
-
-static void __kmp_stg_print_yield_cycle(kmp_str_buf_t *buffer, char const *name,
-                                        void *data) {
-  __kmp_stg_print_bool(buffer, name, __kmp_yield_cycle);
-} // __kmp_stg_print_yield_cycle
-
-static void __kmp_stg_parse_yield_on(char const *name, char const *value,
-                                     void *data) {
-  __kmp_stg_parse_int(name, value, 2, INT_MAX, &__kmp_yield_on_count);
-} // __kmp_stg_parse_yield_on
-
-static void __kmp_stg_print_yield_on(kmp_str_buf_t *buffer, char const *name,
-                                     void *data) {
-  __kmp_stg_print_int(buffer, name, __kmp_yield_on_count);
-} // __kmp_stg_print_yield_on
-
-static void __kmp_stg_parse_yield_off(char const *name, char const *value,
-                                      void *data) {
-  __kmp_stg_parse_int(name, value, 2, INT_MAX, &__kmp_yield_off_count);
-} // __kmp_stg_parse_yield_off
-
-static void __kmp_stg_print_yield_off(kmp_str_buf_t *buffer, char const *name,
-                                      void *data) {
-  __kmp_stg_print_int(buffer, name, __kmp_yield_off_count);
-} // __kmp_stg_print_yield_off
-
 #endif
 
 // -----------------------------------------------------------------------------
-// KMP_INIT_WAIT, KMP_NEXT_WAIT
-
-static void __kmp_stg_parse_init_wait(char const *name, char const *value,
-                                      void *data) {
-  int wait;
-  KMP_ASSERT((__kmp_init_wait & 1) == 0);
-  wait = __kmp_init_wait / 2;
-  __kmp_stg_parse_int(name, value, KMP_MIN_INIT_WAIT, KMP_MAX_INIT_WAIT, &wait);
-  __kmp_init_wait = wait * 2;
-  KMP_ASSERT((__kmp_init_wait & 1) == 0);
-  __kmp_yield_init = __kmp_init_wait;
-} // __kmp_stg_parse_init_wait
-
-static void __kmp_stg_print_init_wait(kmp_str_buf_t *buffer, char const *name,
-                                      void *data) {
-  __kmp_stg_print_int(buffer, name, __kmp_init_wait);
-} // __kmp_stg_print_init_wait
-
-static void __kmp_stg_parse_next_wait(char const *name, char const *value,
-                                      void *data) {
-  int wait;
-  KMP_ASSERT((__kmp_next_wait & 1) == 0);
-  wait = __kmp_next_wait / 2;
-  __kmp_stg_parse_int(name, value, KMP_MIN_NEXT_WAIT, KMP_MAX_NEXT_WAIT, &wait);
-  __kmp_next_wait = wait * 2;
-  KMP_ASSERT((__kmp_next_wait & 1) == 0);
-  __kmp_yield_next = __kmp_next_wait;
-} // __kmp_stg_parse_next_wait
-
-static void __kmp_stg_print_next_wait(kmp_str_buf_t *buffer, char const *name,
-                                      void *data) {
-  __kmp_stg_print_int(buffer, name, __kmp_next_wait);
-} //__kmp_stg_print_next_wait
-
-// -----------------------------------------------------------------------------
 // KMP_GTID_MODE
 
 static void __kmp_stg_parse_gtid_mode(char const *name, char const *value,
                                       void *data) {
   // Modes:
   //   0 -- do not change default
   //   1 -- sp search
   //   2 -- use "keyed" TLS var, i.e.

 
 // Table.
 
 static kmp_setting_t __kmp_stg_table[] = {
 
     {"KMP_ALL_THREADS", __kmp_stg_parse_device_thread_limit, NULL, NULL, 0, 0},
     {"KMP_BLOCKTIME", __kmp_stg_parse_blocktime, __kmp_stg_print_blocktime,
      NULL, 0, 0},
+    {"KMP_USE_YIELD", __kmp_stg_parse_use_yield, __kmp_stg_print_use_yield,
+     NULL, 0, 0},
     {"KMP_DUPLICATE_LIB_OK", __kmp_stg_parse_duplicate_lib_ok,
      __kmp_stg_print_duplicate_lib_ok, NULL, 0, 0},
     {"KMP_LIBRARY", __kmp_stg_parse_wait_policy, __kmp_stg_print_wait_policy,
      NULL, 0, 0},
     {"KMP_DEVICE_THREAD_LIMIT", __kmp_stg_parse_device_thread_limit,
      __kmp_stg_print_device_thread_limit, NULL, 0, 0},
 #if KMP_USE_MONITOR
     {"KMP_MONITOR_STACKSIZE", __kmp_stg_parse_monitor_stacksize,
#ifdef KMP_DEBUG
     {"KMP_DEBUG_BUF_CHARS", __kmp_stg_parse_debug_buf_chars,
      __kmp_stg_print_debug_buf_chars, NULL, 0, 0},
     {"KMP_DEBUG_BUF_LINES", __kmp_stg_parse_debug_buf_lines,
      __kmp_stg_print_debug_buf_lines, NULL, 0, 0},
     {"KMP_DIAG", __kmp_stg_parse_diag, __kmp_stg_print_diag, NULL, 0, 0},
 
     {"KMP_PAR_RANGE", __kmp_stg_parse_par_range_env,
      __kmp_stg_print_par_range_env, NULL, 0, 0},
-    {"KMP_YIELD_CYCLE", __kmp_stg_parse_yield_cycle,
-     __kmp_stg_print_yield_cycle, NULL, 0, 0},
-    {"KMP_YIELD_ON", __kmp_stg_parse_yield_on, __kmp_stg_print_yield_on, NULL,
-     0, 0},
-    {"KMP_YIELD_OFF", __kmp_stg_parse_yield_off, __kmp_stg_print_yield_off,
-     NULL, 0, 0},
 #endif // KMP_DEBUG
 
     {"KMP_ALIGN_ALLOC", __kmp_stg_parse_align_alloc,
      __kmp_stg_print_align_alloc, NULL, 0, 0},
 
     {"KMP_PLAIN_BARRIER", __kmp_stg_parse_barrier_branch_bit,
      __kmp_stg_print_barrier_branch_bit, NULL, 0, 0},
     {"KMP_PLAIN_BARRIER_PATTERN", __kmp_stg_parse_barrier_pattern,
#endif
      __kmp_stg_print_consistency_check, NULL, 0, 0},
 
 #if USE_ITT_BUILD && USE_ITT_NOTIFY
     {"KMP_ITT_PREPARE_DELAY", __kmp_stg_parse_itt_prepare_delay,
      __kmp_stg_print_itt_prepare_delay, NULL, 0, 0},
 #endif /* USE_ITT_BUILD && USE_ITT_NOTIFY */
     {"KMP_MALLOC_POOL_INCR", __kmp_stg_parse_malloc_pool_incr,
      __kmp_stg_print_malloc_pool_incr, NULL, 0, 0},
-    {"KMP_INIT_WAIT", __kmp_stg_parse_init_wait, __kmp_stg_print_init_wait,
-     NULL, 0, 0},
-    {"KMP_NEXT_WAIT", __kmp_stg_parse_next_wait, __kmp_stg_print_next_wait,
-     NULL, 0, 0},
     {"KMP_GTID_MODE", __kmp_stg_parse_gtid_mode, __kmp_stg_print_gtid_mode,
      NULL, 0, 0},
     {"OMP_DYNAMIC", __kmp_stg_parse_omp_dynamic, __kmp_stg_print_omp_dynamic,
      NULL, 0, 0},
     {"KMP_DYNAMIC_MODE", __kmp_stg_parse_kmp_dynamic_mode,
      __kmp_stg_print_kmp_dynamic_mode, NULL, 0, 0},
 
 #ifdef USE_LOAD_BALANCE

openmp/runtime/src/kmp_tasking.cpp

#endif /* USE_ITT_BUILD */
             15,
             ("__kmp_execute_tasks_template: T#%d spin condition satisfied\n",
              gtid));
         return TRUE;
       }
       if (thread->th.th_task_team == NULL) {
         break;
       }
-      // Yield before executing next task
-      KMP_YIELD(__kmp_library == library_throughput);
+      KMP_YIELD(__kmp_library == library_throughput); // Yield before next task
       // If execution of a stolen task results in more tasks being placed on our
       // run queue, reset use_own_tasks
       if (!use_own_tasks && TCR_4(threads_data[tid].td.td_deque_ntasks) != 0) {
         KA_TRACE(20, ("__kmp_execute_tasks_template: T#%d stolen task spawned "
                       "other tasks, restart\n",
                       gtid));
         use_own_tasks = 1;
         new_victim = 0;
#endif
           __kmp_null_resume_wrapper(__kmp_gtid_from_thread(thread), sleep_loc);
         }
       }
     }
     if (done) {
       break;
     }
 
-    // If we are oversubscribed, or have waited a bit (and library mode is
-    // throughput), yield. Pause is in the following code.
-    KMP_YIELD(TCR_4(__kmp_nth) > __kmp_avail_proc);
-    KMP_YIELD_SPIN(spins); // Yields only if KMP_LIBRARY=throughput
+    // If oversubscribed or have waited a bit, yield.
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
   }
 }
 
 // __kmp_task_team_setup:  Create a task_team for the current team, but use
 // an already created, unused one if it already exists.
 void __kmp_task_team_setup(kmp_info_t *this_thr, kmp_team_t *team, int always) {
   KMP_DEBUG_ASSERT(__kmp_tasking_mode != tskm_immediate_exec);
 
#if USE_ITT_BUILD
     KMP_FSYNC_SPIN_PREPARE(RCAST(void *, spin));
 #endif /* USE_ITT_BUILD */
 
     if (TCR_4(__kmp_global.g.g_done)) {
       if (__kmp_global.g.g_abort)
         __kmp_abort_thread();
       break;
     }
-    KMP_YIELD(TRUE); // GH: We always yield here
+    KMP_YIELD(TRUE);
   }
 #if USE_ITT_BUILD
   KMP_FSYNC_SPIN_ACQUIRED(RCAST(void *, spin));
 #endif /* USE_ITT_BUILD */
 }
 
 #if OMP_45_ENABLED
 

openmp/runtime/src/kmp_taskq.cpp

if (!__kmp_threads[gtid]->th.th_team->t.t_serialized) {
 
     /* GEH - need check here under stats to make sure   */
     /*       inside task (curr_thunk[*tid_ref] != NULL) */
 
     my_token = tq->tq_curr_thunk[tid]->th_tasknum;
 
     taskq = tq->tq_curr_thunk[tid]->th.th_shareds->sv_queue;
 
-    KMP_WAIT_YIELD(&taskq->tq_tasknum_serving, my_token, KMP_EQ, NULL);
+    KMP_WAIT(&taskq->tq_tasknum_serving, my_token, KMP_EQ, NULL);
     KMP_MB();
   }
 }
 
 static void __kmp_taskq_xo(int *gtid_ref, int *cid_ref, ident_t *loc_ref) {
   int gtid = *gtid_ref;
   int tid = __kmp_tid_from_gtid(gtid);
   kmp_uint32 my_token;
static void __kmp_taskq_check_ordered(kmp_int32 gtid, kmpc_thunk_t *thunk) {
 
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 
   my_token = thunk->th_tasknum;
 
   taskq = thunk->th.th_shareds->sv_queue;
 
   if (taskq->tq_tasknum_serving <= my_token) {
-    KMP_WAIT_YIELD(&taskq->tq_tasknum_serving, my_token, KMP_GE, NULL);
+    KMP_WAIT(&taskq->tq_tasknum_serving, my_token, KMP_GE, NULL);
     KMP_MB();
     taskq->tq_tasknum_serving = my_token + 1;
     KMP_MB();
   }
 }
 
 #ifdef KMP_DEBUG
 
if (in_parallel) {
     KMP_DEBUG_REF_CTS(
         ("line %d gtid %d: Q %p waiting for ref_count of %d to reach 1\n",
          __LINE__, global_tid, queue, queue->tq_ref_count));
 
     /* wait until all other threads have stopped accessing this queue */
     while (queue->tq_ref_count > 1) {
       __kmp_release_lock(&queue->tq.tq_parent->tq_link_lck, global_tid);
 
-      KMP_WAIT_YIELD((volatile kmp_uint32 *)&queue->tq_ref_count, 1, KMP_LE,
-                     NULL);
+      KMP_WAIT((volatile kmp_uint32 *)&queue->tq_ref_count, 1, KMP_LE, NULL);
 
       __kmp_acquire_lock(&queue->tq.tq_parent->tq_link_lck, global_tid);
       // Make sure data structures are in consistent state before querying them
       // Seems to work without this for digital/alpha, needed for IBM/RS6000
       KMP_MB();
     }
 
     __kmp_release_lock(&queue->tq.tq_parent->tq_link_lck, global_tid);
#endif
   queue = (taskq_thunk == NULL) ? tq->tq_root
                                 : taskq_thunk->th.th_shareds->sv_queue;
 
   KE_TRACE(50, ("__kmpc_end_taskq queue=%p (%d) \n", queue, global_tid));
   is_outermost = (queue == tq->tq_root);
   in_parallel = (queue->tq_flags & TQF_PARALLEL_CONTEXT);
 
   if (in_parallel) {
-    kmp_uint32 spins;
-
     /* this is just a safeguard to release the waiting threads if */
     /* the outermost taskq never queues a task                    */
 
     if (is_outermost && (KMP_MASTER_GTID(global_tid))) {
       if (tq->tq_global_flags & TQF_RELEASE_WORKERS) {
         /* no lock needed, workers are still in spin mode */
         tq->tq_global_flags &= ~TQF_RELEASE_WORKERS;
 
         __kmp_end_split_barrier(bs_plain_barrier, global_tid);
       }
     }
 
     /* keep dequeueing work until all tasks are queued and dequeued */
 
     do {
       /* wait until something is available to dequeue */
-      KMP_INIT_YIELD(spins);
-
       while ((queue->tq_nfull == 0) && (queue->tq_taskq_slot == NULL) &&
              (!__kmp_taskq_has_any_children(queue)) &&
              (!(queue->tq_flags & TQF_ALL_TASKS_QUEUED))) {
-        KMP_YIELD_WHEN(TRUE, spins);
+        KMP_CPU_PAUSE();
       }
 
       /* check to see if we can execute tasks in the queue */
       while (((queue->tq_nfull != 0) || (queue->tq_taskq_slot != NULL)) &&
              (thunk = __kmp_find_task_in_queue(global_tid, queue)) != NULL) {
         KF_TRACE(50, ("Found thunk: %p in primary queue %p (%d)\n", thunk,
                       queue, global_tid));
         __kmp_execute_task_from_queue(tq, loc, global_tid, thunk, in_parallel);
if (!is_outermost) {
 
         return;
       }
 
       __kmp_find_and_remove_finished_child_taskq(tq, global_tid, queue);
 
       /* WAIT until all tasks are finished and no child queues exist before
        * proceeding */
-      KMP_INIT_YIELD(spins);
 
       while (!__kmp_taskq_tasks_finished(queue) ||
              __kmp_taskq_has_any_children(queue)) {
         thunk = __kmp_find_task_in_ancestor_queue(tq, global_tid, queue);
 
         if (thunk != NULL) {
           KF_TRACE(50,
                    ("Stole thunk: %p in ancestor queue: %p while waiting in "
                     "queue: %p (%d)\n",
                     thunk, thunk->th.th_shareds->sv_queue, queue, global_tid));
           __kmp_execute_task_from_queue(tq, loc, global_tid, thunk,
                                         in_parallel);
         }
 
-        KMP_YIELD_WHEN(thunk == NULL, spins);
+        if (thunk == NULL)
+          KMP_CPU_PAUSE();
 
         __kmp_find_and_remove_finished_child_taskq(tq, global_tid, queue);
       }
 
       __kmp_acquire_lock(&queue->tq_queue_lck, global_tid);
       if (!(queue->tq_flags & TQF_DEALLOCATED)) {
         queue->tq_flags |= TQF_DEALLOCATED;
       }
if (!is_outermost) {
           ("__kmpc_end_taskq return for non_outermost queue, wait case (%d)\n",
            global_tid));
 
       return;
     }
 
     // Outermost Queue: steal work from descendants until all tasks are finished
 
-    KMP_INIT_YIELD(spins);
-
     while (!__kmp_taskq_tasks_finished(queue)) {
       thunk = __kmp_find_task_in_descendant_queue(global_tid, queue);
 
       if (thunk != NULL) {
         KF_TRACE(50,
                  ("Stole thunk: %p in descendant queue: %p while waiting in "
                   "queue: %p (%d)\n",
                   thunk, thunk->th.th_shareds->sv_queue, queue, global_tid));
 
         __kmp_execute_task_from_queue(tq, loc, global_tid, thunk, in_parallel);
       }
 
-      KMP_YIELD_WHEN(thunk == NULL, spins);
+      if (thunk == NULL)
+        KMP_CPU_PAUSE();
     }
 
     /* Need this barrier to prevent destruction of queue before threads have all
      * executed above code */
     /* This may need to be done earlier when NOWAIT is implemented for the
      * outermost level */
 
     if (!__kmp_barrier(bs_plain_barrier, global_tid, TRUE, 0, NULL, NULL)) {

openmp/runtime/src/kmp_wait_release.h

if (!KMP_MASTER_TID(ds_tid)) {
       this_thr->th.ompt_thread_info.state = ompt_state_idle;
     } else {
       this_thr->th.ompt_thread_info.state = ompt_state_overhead;
     }
   }
 }
 #endif
 
-/* Spin wait loop that first does pause, then yield, then sleep. A thread that
-   calls __kmp_wait_*  must make certain that another thread calls __kmp_release
+/* Spin wait loop that first does pause/yield, then sleep. A thread that calls
+   __kmp_wait_*  must make certain that another thread calls __kmp_release
    to wake it back up to prevent deadlocks!
 
    NOTE: We may not belong to a team at this point.  */
 template <class C, int final_spin, bool cancellable = false,
           bool sleepable = true>
 static inline bool
 __kmp_wait_template(kmp_info_t *this_thr,
                     C *flag USE_ITT_BUILD_ARG(void *itt_sync_obj)) {
if (ompt_enabled.enabled) {
     if (final_spin && (__kmp_tasking_mode == tskm_immediate_exec ||
                        this_thr->th.th_task_team == NULL)) {
       // implicit task is done. Either no taskqueue, or task-team finished
       __ompt_implicit_task_end(this_thr, ompt_entry_state, tId);
     }
   }
 #endif
 
-  // Setup for waiting
-  KMP_INIT_YIELD(spins);
+  KMP_INIT_YIELD(spins); // Setup for waiting
 
   if (__kmp_dflt_blocktime != KMP_MAX_BLOCKTIME
 #if OMP_50_ENABLED
       || __kmp_pause_status == kmp_soft_paused
 #endif
       ) {
 #if KMP_USE_MONITOR
 // The worker threads cannot rely on the team struct existing at this point.
#endif
     if (TCR_4(__kmp_global.g.g_done)) {
       if (__kmp_global.g.g_abort)
         __kmp_abort_thread();
       break;
     }
 
     // If we are oversubscribed, or have waited a bit (and
     // KMP_LIBRARY=throughput), then yield
-    // TODO: Should it be number of cores instead of thread contexts? Like:
-    // KMP_YIELD(TCR_4(__kmp_nth) > __kmp_ncores);
-    // Need performance improvement data to make the change...
-    if (oversubscribed) {
-      KMP_YIELD(1);
-    } else {
-      KMP_YIELD_SPIN(spins);
-    }
+    KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
+
     // Check if this thread was transferred from a team
     // to the thread pool (or vice-versa) while spinning.
     in_pool = !!TCR_4(this_thr->th.th_in_pool);
     if (in_pool != !!this_thr->th.th_active_in_pool) {
       if (in_pool) { // Recently transferred from team to pool
         KMP_ATOMIC_INC(&__kmp_thread_pool_active_nth);
         this_thr->th.th_active_in_pool = TRUE;
         /* Here, we cannot assert that:

openmp/runtime/src/z_Linux_util.cpp

 #ifdef KMP_CANCEL_THREADS
   KA_TRACE(10, ("__kmp_terminate_thread: kill (%d)\n", gtid));
   status = pthread_cancel(th->th.th_info.ds.ds_thread);
   if (status != 0 && status != ESRCH) {
     __kmp_fatal(KMP_MSG(CantTerminateWorkerThread), KMP_ERR(status),
                 __kmp_msg_null);
   }
 #endif
-  __kmp_yield(TRUE);
+  KMP_YIELD(TRUE);
 } //
 
 /* Set thread stack info according to values returned by pthread_getattr_np().
    If values are unreasonable, assume call failed and use incremental stack
    refinement method instead. Returns TRUE if the stack parameters could be
    determined exactly, FALSE if incremental refinement is necessary. */
 static kmp_int32 __kmp_set_stack_info(int gtid, kmp_info_t *th) {
   int stack_data;

 /* The monitor thread controls all of the threads in the complex */
 
 static void *__kmp_launch_monitor(void *thr) {
   int status, old_type, old_state;
 #ifdef KMP_BLOCK_SIGNALS
   sigset_t new_set;
 #endif /* KMP_BLOCK_SIGNALS */
   struct timespec interval;
-  int yield_count;
-  int yield_cycles = 0;
 
   KMP_MB(); /* Flush all pending memory write invalidates.  */
 
   KA_TRACE(10, ("__kmp_launch_monitor: #1 launched\n"));
 
   /* register us as the monitor thread */
   __kmp_gtid_set_specific(KMP_GTID_MONITOR);
 #ifdef KMP_TDATA_GTID
if (__kmp_monitor_wakeups == 1) {
     interval.tv_nsec = 0;
   } else {
     interval.tv_sec = 0;
     interval.tv_nsec = (KMP_NSEC_PER_SEC / __kmp_monitor_wakeups);
   }
 
   KA_TRACE(10, ("__kmp_launch_monitor: #2 monitor\n"));
 
-  if (__kmp_yield_cycle) {
-    __kmp_yielding_on = 0; /* Start out with yielding shut off */
-    yield_count = __kmp_yield_off_count;
-  } else {
-    __kmp_yielding_on = 1; /* Yielding is on permanently */
-  }
-
   while (!TCR_4(__kmp_global.g.g_done)) {
     struct timespec now;
     struct timeval tval;
 
     /*  This thread monitors the state of the system */
 
     KA_TRACE(15, ("__kmp_launch_monitor: update\n"));
 
if (!TCR_4(__kmp_global.g.g_done)) { // check once more under mutex
         if (status != ETIMEDOUT && status != EINTR) {
           KMP_SYSFAIL("pthread_cond_timedwait", status);
         }
       }
     }
     status = pthread_mutex_unlock(&__kmp_wait_mx.m_mutex);
     KMP_CHECK_SYSFAIL("pthread_mutex_unlock", status);
 
-    if (__kmp_yield_cycle) {
-      yield_cycles++;
-      if ((yield_cycles % yield_count) == 0) {
-        if (__kmp_yielding_on) {
-          __kmp_yielding_on = 0; /* Turn it off now */
-          yield_count = __kmp_yield_off_count;
-        } else {
-          __kmp_yielding_on = 1; /* Turn it on now */
-          yield_count = __kmp_yield_on_count;
-        }
-        yield_cycles = 0;
-      }
-    } else {
-      __kmp_yielding_on = 1;
-    }
-
     TCW_4(__kmp_global.g.g_time.dt.t_value,
           TCR_4(__kmp_global.g.g_time.dt.t_value) + 1);
 
     KMP_MB(); /* Flush all pending memory write invalidates.  */
   }
 
   KA_TRACE(10, ("__kmp_launch_monitor: #3 cleanup\n"));
 
#endif /* _POSIX_THREAD_ATTR_STACKSIZE */
   }
 
   th->th.th_info.ds.ds_thread = handle;
 
 #if KMP_REAL_TIME_FIX
   // Wait for the monitor thread is really started and set its *priority*.
   KMP_DEBUG_ASSERT(sizeof(kmp_uint32) ==
                    sizeof(__kmp_global.g.g_time.dt.t_value));
-  __kmp_wait_yield_4((kmp_uint32 volatile *)&__kmp_global.g.g_time.dt.t_value,
-                     -1, &__kmp_neq_4, NULL);
+  __kmp_wait_4((kmp_uint32 volatile *)&__kmp_global.g.g_time.dt.t_value, -1,
+               &__kmp_neq_4, NULL);
 #endif // KMP_REAL_TIME_FIX
 
 #ifdef KMP_THREAD_ATTR
   status = pthread_attr_destroy(&thread_attr);
   if (status != 0) {
     kmp_msg_t err_code = KMP_ERR(status);
     __kmp_msg(kmp_ms_warning, KMP_MSG(CantDestroyThreadAttrs), err_code,
               __kmp_msg_null);
#endif
   status = pthread_mutex_unlock(&__kmp_wait_mx.m_mutex);
   KMP_CHECK_SYSFAIL("pthread_mutex_unlock", status);
   KF_TRACE(30, ("__kmp_resume_monitor: T#%d exiting after signaling wake up"
                 " for T#%d\n",
                 gtid, KMP_GTID_MONITOR));
 }
 #endif // KMP_USE_MONITOR
 
-void __kmp_yield(int cond) {
-  if (!cond)
-    return;
-#if KMP_USE_MONITOR
-  if (!__kmp_yielding_on)
-    return;
-#else
-  if (__kmp_yield_cycle && !KMP_YIELD_NOW())
-    return;
-#endif
-  sched_yield();
-}
+void __kmp_yield() { sched_yield(); }
 
 void __kmp_gtid_set_specific(int gtid) {
   if (__kmp_init_gtid) {
     int status;
     status = pthread_setspecific(__kmp_gtid_threadprivate_key,
                                  (void *)(intptr_t)(gtid + 1));
     KMP_CHECK_SYSFAIL("pthread_setspecific", status);
   } else {

openmp/runtime/src/z_Windows_NT_util.cpp

 }
 void __kmp_resume_64(int target_gtid, kmp_flag_64 *flag) {
   __kmp_resume_template(target_gtid, flag);
 }
 void __kmp_resume_oncore(int target_gtid, kmp_flag_oncore *flag) {
   __kmp_resume_template(target_gtid, flag);
 }
 
-void __kmp_yield(int cond) {
-  if (cond)
-    Sleep(0);
-}
+void __kmp_yield() { Sleep(0); }
 
 void __kmp_gtid_set_specific(int gtid) {
   if (__kmp_init_gtid) {
     KA_TRACE(50, ("__kmp_gtid_set_specific: T#%d key:%d\n", gtid,
                   __kmp_gtid_threadprivate_key));
     if (!TlsSetValue(__kmp_gtid_threadprivate_key, (LPVOID)(gtid + 1)))
       KMP_FATAL(TLSSetValueFailed);
   } else {
/* 2006-10-19:
      1. Windows* OS keep thread alive after it resets ds_alive flag and
      exits from thread function. (For example, see C70770/Q394281 "unloading of
      dll based on OMP is very slow".)
      2. Windows* OS may kill thread before it resets ds_alive flag.
 
      Right solution seems to be waiting for *either* thread termination *or*
      ds_alive resetting. */
   {
-    // TODO: This code is very similar to KMP_WAIT_YIELD. Need to generalize
-    // KMP_WAIT_YIELD to cover this usage also.
+    // TODO: This code is very similar to KMP_WAIT. Need to generalize
+    // KMP_WAIT to cover this usage also.
     void *obj = NULL;
     kmp_uint32 spins;
 #if USE_ITT_BUILD
     KMP_FSYNC_SPIN_INIT(obj, (void *)&th->th.th_info.ds.ds_alive);
 #endif /* USE_ITT_BUILD */
     KMP_INIT_YIELD(spins);
     do {
 #if USE_ITT_BUILD
       KMP_FSYNC_SPIN_PREPARE(obj);
 #endif /* USE_ITT_BUILD */
       __kmp_is_thread_alive(th, &exit_val);
-      KMP_YIELD(TCR_4(__kmp_nth) > __kmp_avail_proc);
-      KMP_YIELD_SPIN(spins);
+      KMP_YIELD_OVERSUB_ELSE_SPIN(spins);
     } while (exit_val == STILL_ACTIVE && TCR_4(th->th.th_info.ds.ds_alive));
 #if USE_ITT_BUILD
     if (exit_val == STILL_ACTIVE) {
       KMP_FSYNC_CANCEL(obj);
     } else {
       KMP_FSYNC_SPIN_ACQUIRED(obj);
     }
 #endif /* USE_ITT_BUILD */