[OPENMP] Implementation of omp_get_default_device and omp_set_default_device

[grokos]

Summary

Implementation of missing OpenMP 4.0 API functions omp_get_default_device and omp_set_default_device.
Also, added support for the environment variable OMP_DEFAULT_DEVICE.

[AndreyChurbanov]

I suggest moving the ICV into kmp_internal_control structure, thus its propagation from parent to children is automatically maintained everywhere in the library code.

runtime/src/kmp.h

2253 ↗

(On Diff #68277)

This does not look like a good location for the ICV. Is it better to place it along with other per-task ICVs in the td_icvs structure? Thus it will be automatically maintained at each task creation using appropriate mechanism.

runtime/src/kmp_ftn_entry.h

907 ↗

(On Diff #68277)

Why KMP_STUB is removed here? Empty routines should continue to work fine for the stubs library I think.

runtime/src/kmp_tasking.c

864 ↗

(On Diff #68277)

This looks wrong, as the ICV should be inherited from the parent task (if any). As I written below, the ICV should better be placed and initialized along with other per-task ICVs. Then global value can be assigned in __kmp_get_global_icvs() function.

[Hahnfeld]

In general: Do we really need this in libomp? We currently have the problem of two runtime libraries and will probably continue with it: libomp supporting the host and liboffload / libomptarget supporting all target related things.

I imagine in the current state this will give linker errors with liboffload / libomptarget that define their own version of this function.

[AndreyChurbanov]

In D23587#517940, @Hahnfeld wrote:

In general: Do we really need this in libomp?

Not necessarily, but this looks like an appropriate solution - to move the functions from offload library to libomp.

We currently have the problem of two runtime libraries and will probably continue with it: libomp supporting the host and liboffload / libomptarget supporting all target related things.

I imagine in the current state this will give linker errors with liboffload / libomptarget that define their own version of this function.

It is unlikely because the functions supposed to be removed from offload library simultaneously, at list this is an intention.

An alternative would be to implement internal versions of the functions in libomp leaving public symbols in offload library and changing their implementation to call to libomp, but this also does not look very elegant solution.

The initial problem might be clearer specified in the summary, as it is not an implementation of missing functions, it is the (part of) movement of incorrectly implemented functions to place where they can easier be implemented correctly. The offload library does not mange OMP tasks and thus it can hardly implement per-task control in a correct way without help of libomp.

[grokos]

I fixed the issues Andrey mentioned.

[grokos]

In D23587#517940, @Hahnfeld wrote:

I imagine in the current state this will give linker errors with liboffload / libomptarget that define their own version of this function.

As discussed last week, libomptarget does not implement these two functions. The 4.0 standard mandates that the default device is set per-task. libomptarget (and liboffload as far as I understand) has no notion of tasks, so implementing those functions anywhere else than libomp would be problematic.

runtime/src/kmp_ftn_entry.h

907 ↗

(On Diff #68277)

Right, I had misunderstood the role of KMP_STUB. I restored it and merged both versions of each routine into a single function, following the style of other API functions.

[Hahnfeld]

In D23587#518589, @grokos wrote:

As discussed last week, libomptarget does not implement these two functions. The 4.0 standard mandates that the default device is set per-task. libomptarget (and liboffload as far as I understand) has no notion of tasks, so implementing those functions anywhere else than libomp would be problematic.

Hmm, that wasn't really part of the discussion but anyway I now understand why this has to be done here (I was under the impression that there would only be one default-device-var per program).

I assume you will then call omp_get_default_device() from within the libomptarget?

[AndreyChurbanov]

LGTM

[grokos]

In D23587#519095, @Hahnfeld wrote:

I assume you will then call omp_get_default_device() from within the libomptarget?

Exactly.

openmp/trunk/runtime/src/dllexports

%ifdef OMP_40
     omp_get_proc_bind                       862
    #omp_set_proc_bind                       863
    #omp_curr_proc_bind                      864
     omp_get_num_teams                       865
     omp_get_team_num                        866
     omp_get_cancellation                    867
     kmp_get_cancellation_status             868
     omp_is_initial_device                   869
-    %ifdef stub
-        omp_set_default_device              879
-        omp_get_default_device              880
+    omp_set_default_device                  879
+    omp_get_default_device                  880
+    %ifdef stub
         omp_get_num_devices                 881
     %endif
 %endif # OMP_40
 
 # OpenMP 45
 
 %ifdef OMP_45
     omp_init_lock_with_hint                 870

openmp/trunk/runtime/src/kmp.h

 #define KMP_MAX_ORDERED         8
 
 #define KMP_MAX_FIELDS          32
 
 #define KMP_MAX_BRANCH_BITS     31
 
 #define KMP_MAX_ACTIVE_LEVELS_LIMIT INT_MAX
 
+#define KMP_MAX_DEFAULT_DEVICE_LIMIT INT_MAX
+
 #define KMP_MAX_TASK_PRIORITY_LIMIT INT_MAX
 
 /* Minimum number of threads before switch to TLS gtid (experimentally determined) */
 /* josh TODO: what about OS X* tuning? */
 #if   KMP_ARCH_X86 || KMP_ARCH_X86_64
 # define KMP_TLS_GTID_MIN     5
 #else
 # define KMP_TLS_GTID_MIN     INT_MAX
typedef struct kmp_internal_control {
     kmp_int8      bt_set;                /* internal control for whether blocktime is explicitly set */
     int           blocktime;             /* internal control for blocktime */
     int           bt_intervals;          /* internal control for blocktime intervals */
     int           nproc;                 /* internal control for #threads for next parallel region (per thread) */
     int           max_active_levels;     /* internal control for max_active_levels */
     kmp_r_sched_t sched;                 /* internal control for runtime schedule {sched,chunk} pair */
 #if OMP_40_ENABLED
     kmp_proc_bind_t proc_bind;           /* internal control for affinity  */
+    kmp_int32       default_device;      /* internal control for default device */
 #endif // OMP_40_ENABLED
     struct kmp_internal_control *next;
 } kmp_internal_control_t;
 
 static inline void
 copy_icvs( kmp_internal_control_t *dst, kmp_internal_control_t *src ) {
     *dst = *src;
 }
typedef enum kmp_tasking_mode {
     tskm_immediate_exec = 0,
     tskm_extra_barrier = 1,
     tskm_task_teams = 2,
     tskm_max = 2
 } kmp_tasking_mode_t;
 
 extern kmp_tasking_mode_t __kmp_tasking_mode;         /* determines how/when to execute tasks */
 extern kmp_int32 __kmp_task_stealing_constraint;
+#if OMP_40_ENABLED
+    extern kmp_int32 __kmp_default_device; // Set via OMP_DEFAULT_DEVICE if specified, defaults to 0 otherwise
+#endif
 #if OMP_45_ENABLED
     extern kmp_int32 __kmp_max_task_priority; // Set via OMP_MAX_TASK_PRIORITY if specified, defaults to 0 otherwise
 #endif
 
 /* NOTE: kmp_taskdata_t and kmp_task_t structures allocated in single block with taskdata first */
 #define KMP_TASK_TO_TASKDATA(task)     (((kmp_taskdata_t *) task) - 1)
 #define KMP_TASKDATA_TO_TASK(taskdata) (kmp_task_t *) (taskdata + 1)
 

openmp/trunk/runtime/src/kmp_ftn_entry.h

#else
                 return team->t.t_master_tid;
             }
         } else {
             return 0;
         }
     #endif
 }
 
-#if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
-
 int FTN_STDCALL
-FTN_GET_DEFAULT_DEVICE( void )
+xexpand(FTN_GET_DEFAULT_DEVICE)( void )
 {
+    #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
         return 0;
+    #else
+        return __kmp_entry_thread() -> th.th_current_task -> td_icvs.default_device;
+    #endif
 }
 
 void FTN_STDCALL
-FTN_SET_DEFAULT_DEVICE( int KMP_DEREF arg )
+xexpand(FTN_SET_DEFAULT_DEVICE)( int KMP_DEREF arg )
 {
+    #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
+    // Nothing.
+    #else
+        __kmp_entry_thread() -> th.th_current_task -> td_icvs.default_device = KMP_DEREF arg;
+    #endif
 }
 
+#if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
+
 int FTN_STDCALL
 FTN_GET_NUM_DEVICES( void )
 {
     return 0;
 }
 
 #endif // KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
 

 xaliasify(FTN_IN_FINAL, 31);
 
 #if OMP_40_ENABLED
 // OMP_4.0 aliases
 xaliasify(FTN_GET_PROC_BIND, 40);
 xaliasify(FTN_GET_NUM_TEAMS, 40);
 xaliasify(FTN_GET_TEAM_NUM, 40);
 xaliasify(FTN_GET_CANCELLATION, 40);
+xaliasify(FTN_GET_DEFAULT_DEVICE, 40);
+xaliasify(FTN_SET_DEFAULT_DEVICE, 40);
 xaliasify(FTN_IS_INITIAL_DEVICE, 40);
 #endif /* OMP_40_ENABLED */
 
 #if OMP_45_ENABLED
 // OMP_4.5 aliases
 #endif
 
 #if OMP_50_ENABLED

 xversionify(FTN_TEST_LOCK,         30, "OMP_3.0");
 xversionify(FTN_TEST_NEST_LOCK,    30, "OMP_3.0");
 
 // OMP_3.1 versioned symbol
 xversionify(FTN_IN_FINAL,          31, "OMP_3.1");
 
 #if OMP_40_ENABLED
 // OMP_4.0 versioned symbols
-xversionify(FTN_GET_PROC_BIND,     40, "OMP_4.0");
-xversionify(FTN_GET_NUM_TEAMS,     40, "OMP_4.0");
-xversionify(FTN_GET_TEAM_NUM,      40, "OMP_4.0");
-xversionify(FTN_GET_CANCELLATION,  40, "OMP_4.0");
-xversionify(FTN_IS_INITIAL_DEVICE, 40, "OMP_4.0");
+xversionify(FTN_GET_PROC_BIND,      40, "OMP_4.0");
+xversionify(FTN_GET_NUM_TEAMS,      40, "OMP_4.0");
+xversionify(FTN_GET_TEAM_NUM,       40, "OMP_4.0");
+xversionify(FTN_GET_CANCELLATION,   40, "OMP_4.0");
+xversionify(FTN_GET_DEFAULT_DEVICE, 40, "OMP_4.0");
+xversionify(FTN_SET_DEFAULT_DEVICE, 40, "OMP_4.0");
+xversionify(FTN_IS_INITIAL_DEVICE,  40, "OMP_4.0");
 #endif /* OMP_40_ENABLED */
 
 #if OMP_45_ENABLED
 // OMP_4.5 versioned symbols
 #endif
 
 #if OMP_50_ENABLED
 // OMP_5.0 versioned symbols

openmp/trunk/runtime/src/kmp_ftn_os.h

#endif
     #define FTN_SET_WARNINGS_ON                  kmp_set_warnings_on
     #define FTN_SET_WARNINGS_OFF                 kmp_set_warnings_off
 
     #define FTN_GET_WTIME                        omp_get_wtime
     #define FTN_GET_WTICK                        omp_get_wtick
 
 #if OMP_40_ENABLED
 #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
-    #define FTN_GET_DEFAULT_DEVICE               omp_get_default_device
-    #define FTN_SET_DEFAULT_DEVICE               omp_set_default_device
     #define FTN_GET_NUM_DEVICES                  omp_get_num_devices
 #endif
+    #define FTN_GET_DEFAULT_DEVICE               omp_get_default_device
+    #define FTN_SET_DEFAULT_DEVICE               omp_set_default_device
     #define FTN_IS_INITIAL_DEVICE                omp_is_initial_device
 #endif
 
 #if OMP_40_ENABLED
     #define FTN_GET_CANCELLATION                 omp_get_cancellation
     #define FTN_GET_CANCELLATION_STATUS          kmp_get_cancellation_status
 #endif
 
#endif
     #define FTN_SET_WARNINGS_ON                  kmp_set_warnings_on_
     #define FTN_SET_WARNINGS_OFF                 kmp_set_warnings_off_
 
     #define FTN_GET_WTIME                        omp_get_wtime_
     #define FTN_GET_WTICK                        omp_get_wtick_
 
 #if OMP_40_ENABLED
 #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
-    #define FTN_GET_DEFAULT_DEVICE               omp_get_default_device_
-    #define FTN_SET_DEFAULT_DEVICE               omp_set_default_device_
     #define FTN_GET_NUM_DEVICES                  omp_get_num_devices_
 #endif
+    #define FTN_GET_DEFAULT_DEVICE               omp_get_default_device_
+    #define FTN_SET_DEFAULT_DEVICE               omp_set_default_device_
     #define FTN_IS_INITIAL_DEVICE                omp_is_initial_device_
 #endif
 
 
 #if OMP_40_ENABLED
     #define FTN_GET_CANCELLATION                 omp_get_cancellation_
     #define FTN_GET_CANCELLATION_STATUS          kmp_get_cancellation_status_
 #endif
#endif
     #define FTN_SET_WARNINGS_ON                  KMP_SET_WARNINGS_ON
     #define FTN_SET_WARNINGS_OFF                 KMP_SET_WARNINGS_OFF
 
     #define FTN_GET_WTIME                        OMP_GET_WTIME
     #define FTN_GET_WTICK                        OMP_GET_WTICK
 
 #if OMP_40_ENABLED
 #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
-    #define FTN_GET_DEFAULT_DEVICE               OMP_GET_DEFAULT_DEVICE
-    #define FTN_SET_DEFAULT_DEVICE               OMP_SET_DEFAULT_DEVICE
     #define FTN_GET_NUM_DEVICES                  OMP_GET_NUM_DEVICES
 #endif
+    #define FTN_GET_DEFAULT_DEVICE               OMP_GET_DEFAULT_DEVICE
+    #define FTN_SET_DEFAULT_DEVICE               OMP_SET_DEFAULT_DEVICE
     #define FTN_IS_INITIAL_DEVICE                OMP_IS_INITIAL_DEVICE
 #endif
 
 
 #if OMP_40_ENABLED
     #define FTN_GET_CANCELLATION                 OMP_GET_CANCELLATION
     #define FTN_GET_CANCELLATION_STATUS          KMP_GET_CANCELLATION_STATUS
 #endif
#endif
     #define FTN_SET_WARNINGS_ON                  KMP_SET_WARNINGS_ON_
     #define FTN_SET_WARNINGS_OFF                 KMP_SET_WARNINGS_OFF_
 
     #define FTN_GET_WTIME                        OMP_GET_WTIME_
     #define FTN_GET_WTICK                        OMP_GET_WTICK_
 
 #if OMP_40_ENABLED
 #if KMP_MIC || KMP_OS_DARWIN || defined(KMP_STUB)
-    #define FTN_GET_DEFAULT_DEVICE               OMP_GET_DEFAULT_DEVICE_
-    #define FTN_SET_DEFAULT_DEVICE               OMP_SET_DEFAULT_DEVICE_
     #define FTN_GET_NUM_DEVICES                  OMP_GET_NUM_DEVICES_
 #endif
+    #define FTN_GET_DEFAULT_DEVICE               OMP_GET_DEFAULT_DEVICE_
+    #define FTN_SET_DEFAULT_DEVICE               OMP_SET_DEFAULT_DEVICE_
     #define FTN_IS_INITIAL_DEVICE                OMP_IS_INITIAL_DEVICE_
 #endif
 
 
 #if OMP_40_ENABLED
     #define FTN_GET_CANCELLATION                 OMP_GET_CANCELLATION_
     #define FTN_GET_CANCELLATION_STATUS          KMP_GET_CANCELLATION_STATUS_
 #endif

openmp/trunk/runtime/src/kmp_global.c

 #endif
 
 int __kmp_place_num_sockets = 0;
 int __kmp_place_socket_offset = 0;
 int __kmp_place_num_cores = 0;
 int __kmp_place_core_offset = 0;
 int __kmp_place_num_threads_per_core = 0;
 
+#if OMP_40_ENABLED
+kmp_int32 __kmp_default_device = 0;
+#endif
+
 kmp_tasking_mode_t __kmp_tasking_mode = tskm_task_teams;
 #if OMP_45_ENABLED
 kmp_int32 __kmp_max_task_priority = 0;
 #endif
 
 /* This check ensures that the compiler is passing the correct data type
  * for the flags formal parameter of the function kmpc_omp_task_alloc().
  * If the type is not a 4-byte type, then give an error message about

openmp/trunk/runtime/src/kmp_runtime.c

kmp_internal_control_t g_icvs = {
       __kmp_dflt_blocktime,         //int blocktime;            //internal control for blocktime
       __kmp_bt_intervals,           //int bt_intervals;         //internal control for blocktime intervals
       __kmp_dflt_team_nth,          //int nproc;                //internal control for # of threads for next parallel region (per thread)
                                     // (use a max ub on value if __kmp_parallel_initialize not called yet)
       __kmp_dflt_max_active_levels, //int max_active_levels;    //internal control for max_active_levels
       r_sched,                      //kmp_r_sched_t sched;      //internal control for runtime schedule {sched,chunk} pair
 #if OMP_40_ENABLED
       __kmp_nested_proc_bind.bind_types[0],
+      __kmp_default_device,
 #endif /* OMP_40_ENABLED */
       NULL                          //struct kmp_internal_control *next;
     };
 
     return g_icvs;
 }
 
 static kmp_internal_control_t

openmp/trunk/runtime/src/kmp_settings.c

__kmp_stg_parse_max_active_levels( char const * name, char const * value, void * data ) {
     __kmp_stg_parse_int( name, value, 0, KMP_MAX_ACTIVE_LEVELS_LIMIT, & __kmp_dflt_max_active_levels );
 } // __kmp_stg_parse_max_active_levels
 
 static void
 __kmp_stg_print_max_active_levels( kmp_str_buf_t * buffer, char const * name, void * data ) {
     __kmp_stg_print_int( buffer, name, __kmp_dflt_max_active_levels );
 } // __kmp_stg_print_max_active_levels
 
+#if OMP_40_ENABLED
+// -------------------------------------------------------------------------------------------------
+// OpenMP 4.0: OMP_DEFAULT_DEVICE
+// -------------------------------------------------------------------------------------------------
+static void __kmp_stg_parse_default_device(char const *name, char const *value, void *data) {
+  __kmp_stg_parse_int(name, value, 0, KMP_MAX_DEFAULT_DEVICE_LIMIT, &__kmp_default_device);
+} // __kmp_stg_parse_default_device
+
+static void __kmp_stg_print_default_device(kmp_str_buf_t *buffer, char const *name, void *data) {
+  __kmp_stg_print_int(buffer, name, __kmp_default_device);
+} // __kmp_stg_print_default_device
+#endif
+
 #if OMP_45_ENABLED
 // -------------------------------------------------------------------------------------------------
 // OpenMP 4.5: OMP_MAX_TASK_PRIORITY
 // -------------------------------------------------------------------------------------------------
 static void
 __kmp_stg_parse_max_task_priority(char const *name, char const *value, void *data) {
     __kmp_stg_parse_int(name, value, 0, KMP_MAX_TASK_PRIORITY_LIMIT, &__kmp_max_task_priority);
 } // __kmp_stg_parse_max_task_priority
static kmp_setting_t __kmp_stg_table[] = {
 
     { "OMP_NESTED",                        __kmp_stg_parse_nested,             __kmp_stg_print_nested,             NULL, 0, 0 },
     { "OMP_NUM_THREADS",                   __kmp_stg_parse_num_threads,        __kmp_stg_print_num_threads,        NULL, 0, 0 },
     { "OMP_STACKSIZE",                     __kmp_stg_parse_stacksize,          __kmp_stg_print_stacksize,          NULL, 0, 0 },
 
     { "KMP_TASKING",                       __kmp_stg_parse_tasking,            __kmp_stg_print_tasking,            NULL, 0, 0 },
     { "KMP_TASK_STEALING_CONSTRAINT",      __kmp_stg_parse_task_stealing,      __kmp_stg_print_task_stealing,      NULL, 0, 0 },
     { "OMP_MAX_ACTIVE_LEVELS",             __kmp_stg_parse_max_active_levels,  __kmp_stg_print_max_active_levels,  NULL, 0, 0 },
+#if OMP_40_ENABLED
+    { "OMP_DEFAULT_DEVICE",                __kmp_stg_parse_default_device,     __kmp_stg_print_default_device,     NULL, 0, 0 },
+#endif
 #if OMP_45_ENABLED
     { "OMP_MAX_TASK_PRIORITY",             __kmp_stg_parse_max_task_priority,  __kmp_stg_print_max_task_priority,  NULL, 0, 0 },
 #endif
     { "OMP_THREAD_LIMIT",                  __kmp_stg_parse_all_threads,        __kmp_stg_print_all_threads,        NULL, 0, 0 },
     { "OMP_WAIT_POLICY",                   __kmp_stg_parse_wait_policy,        __kmp_stg_print_wait_policy,        NULL, 0, 0 },
     { "KMP_DISP_NUM_BUFFERS",              __kmp_stg_parse_disp_buffers,       __kmp_stg_print_disp_buffers,       NULL, 0, 0 },
 #if KMP_NESTED_HOT_TEAMS
     { "KMP_HOT_TEAMS_MAX_LEVEL",           __kmp_stg_parse_hot_teams_level,    __kmp_stg_print_hot_teams_level,    NULL, 0, 0 },