[OpenMP] Add upper limit to TPAUSE exponential backoff time

[jdoerfert]

LG

openmp/runtime/src/kmp.h

#define KMP_YIELD_SPIN(count)                                                  \
   }
 
 // If TPAUSE is available & enabled, use it. If oversubscribed, use the slower
 // (C0.2) state, which improves performance of other SMT threads on the same
 // core, otherwise, use the fast (C0.1) default state, or whatever the user has
 // requested. Uses a timed TPAUSE, and exponential backoff. If TPAUSE isn't
 // available, fall back to the regular CPU pause and yield combination.
 #if KMP_HAVE_UMWAIT
+#define KMP_TPAUSE_MAX_MASK ((kmp_uint64)0xFFFF)
 #define KMP_YIELD_OVERSUB_ELSE_SPIN(count, time)                               \
   {                                                                            \
     if (__kmp_tpause_enabled) {                                                \
       if (KMP_OVERSUBSCRIBED) {                                                \
         __kmp_tpause(0, (time));                                               \
       } else {                                                                 \
         __kmp_tpause(__kmp_tpause_hint, (time));                               \
       }                                                                        \
-      (time) *= 2;                                                             \
+      (time) = (time << 1 | 1) & KMP_TPAUSE_MAX_MASK;                          \
     } else {                                                                   \
       KMP_CPU_PAUSE();                                                         \
       if ((KMP_TRY_YIELD_OVERSUB)) {                                           \
         __kmp_yield();                                                         \
       } else if (__kmp_use_yield == 1) {                                       \
         (count) -= 2;                                                          \
         if (!(count)) {                                                        \
           __kmp_yield();                                                       \