[Openmp-commits] [PATCH] D106572: [OpenMP] Refined the logic to give a regular task from a hidden helper task

[Shilei Tian via Phabricator via Openmp-commits]

tianshilei1992 created this revision.
tianshilei1992 added reviewers: AndreyChurbanov, hbae, protze.joachim.
Herald added subscribers: guansong, yaxunl.
tianshilei1992 requested review of this revision.
Herald added a reviewer: jdoerfert.
Herald added subscribers: openmp-commits, sstefan1.
Herald added a project: OpenMP.

In current implementation, if a regular task depends on a hidden helper task,
and when the hidden helper task is releasing its dependences, it directly calls
`__kmp_omp_task`. This could cause a problem that if `__kmp_push_task` returns
`TASK_NOT_PUSHED`, the task will be executed immediately. However, the hidden
helper threads are assumed to only execute hidden helper tasks. This could cause
problems because when calling `__kmp_omp_task`, the encountering gtid, which is
not the real one of the thread, is passed.

This patch uses `__kmp_give_task`, but because it is a static function, a new
wrapper `__kmpc_give_task` is added.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106572

Files:
  openmp/runtime/src/kmp_taskdeps.h
  openmp/runtime/src/kmp_tasking.cpp


Index: openmp/runtime/src/kmp_tasking.cpp
===================================================================
--- openmp/runtime/src/kmp_tasking.cpp
+++ openmp/runtime/src/kmp_tasking.cpp
@@ -3920,6 +3920,34 @@
             gtid, taskdata));
 }
 
+void __kmpc_give_task(kmp_task_t *ptask, kmp_int32 start = 0) {
+  KMP_DEBUG_ASSERT(ptask != NULL);
+  kmp_taskdata_t *taskdata = KMP_TASK_TO_TASKDATA(ptask);
+
+  // Enqueue task to complete bottom half completion from a thread within the
+  // corresponding team
+  kmp_team_t *team = taskdata->td_team;
+  kmp_int32 nthreads = team->t.t_nproc;
+  kmp_info_t *thread;
+
+  // This should be similar to start_k = __kmp_get_random( thread ) % nthreads
+  // but we cannot use __kmp_get_random here
+  kmp_int32 start_k = start;
+  kmp_int32 pass = 1;
+  kmp_int32 k = start_k;
+
+  do {
+    // For now we're just linearly trying to find a thread
+    thread = team->t.t_threads[k];
+    k = (k + 1) % nthreads;
+
+    // we did a full pass through all the threads
+    if (k == start_k)
+      pass = pass << 1;
+
+  } while (!__kmp_give_task(thread, k, ptask, pass));
+}
+
 /*!
 @ingroup TASKING
 @param ptask Task which execution is completed
@@ -3940,28 +3968,7 @@
 
   __kmp_first_top_half_finish_proxy(taskdata);
 
-  // Enqueue task to complete bottom half completion from a thread within the
-  // corresponding team
-  kmp_team_t *team = taskdata->td_team;
-  kmp_int32 nthreads = team->t.t_nproc;
-  kmp_info_t *thread;
-
-  // This should be similar to start_k = __kmp_get_random( thread ) % nthreads
-  // but we cannot use __kmp_get_random here
-  kmp_int32 start_k = 0;
-  kmp_int32 pass = 1;
-  kmp_int32 k = start_k;
-
-  do {
-    // For now we're just linearly trying to find a thread
-    thread = team->t.t_threads[k];
-    k = (k + 1) % nthreads;
-
-    // we did a full pass through all the threads
-    if (k == start_k)
-      pass = pass << 1;
-
-  } while (!__kmp_give_task(thread, k, ptask, pass));
+  __kmpc_give_task(ptask);
 
   __kmp_second_top_half_finish_proxy(taskdata);
 
Index: openmp/runtime/src/kmp_taskdeps.h
===================================================================
--- openmp/runtime/src/kmp_taskdeps.h
+++ openmp/runtime/src/kmp_taskdeps.h
@@ -85,6 +85,8 @@
 #endif
 }
 
+extern void __kmpc_give_task(kmp_task_t *ptask, kmp_int32 start);
+
 static inline void __kmp_release_deps(kmp_int32 gtid, kmp_taskdata_t *task) {
   kmp_info_t *thread = __kmp_threads[gtid];
   kmp_depnode_t *node = task->td_depnode;
@@ -143,7 +145,9 @@
           // encountering thread's queue; otherwise, it can be pushed to its own
           // queue.
           if (!next_taskdata->td_flags.hidden_helper) {
-            __kmp_omp_task(task->encountering_gtid, successor->dn.task, false);
+            __kmpc_give_task(
+                successor->dn.task,
+                __kmp_tid_from_gtid(next_taskdata->encountering_gtid));
           } else {
             __kmp_omp_task(gtid, successor->dn.task, false);
           }


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