[Openmp-commits] [openmp] r266675 - Runtime support for untied tasks

[Jonathan Peyton via Openmp-commits]

Author: jlpeyton
Date: Mon Apr 18 16:35:14 2016
New Revision: 266675

URL: http://llvm.org/viewvc/llvm-project?rev=266675&view=rev
Log:
Runtime support for untied tasks

Introduced a counter of parts of an untied task submitted for execution. The
counter controls whether all parts of the task are already finished. The
compiler should generate re-submission of partially executed untied task by
itself before exiting of each task part except for the lexical last part.

Differential Revision: http://reviews.llvm.org/D19026

Modified:
    openmp/trunk/runtime/src/kmp.h
    openmp/trunk/runtime/src/kmp_tasking.c

Modified: openmp/trunk/runtime/src/kmp.h
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp.h?rev=266675&r1=266674&r2=266675&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp.h (original)
+++ openmp/trunk/runtime/src/kmp.h Mon Apr 18 16:35:14 2016
@@ -2189,6 +2189,7 @@ struct kmp_taskdata {
                                                       /* Currently not used except for perhaps IDB */
     kmp_taskdata_t *        td_parent;                /* parent task                             */
     kmp_int32               td_level;                 /* task nesting level                      */
+    kmp_int32               td_untied_count;          /* untied task active parts counter        */
     ident_t *               td_ident;                 /* task identifier                         */
                             // Taskwait data.
     ident_t *               td_taskwait_ident;

Modified: openmp/trunk/runtime/src/kmp_tasking.c
URL: http://llvm.org/viewvc/llvm-project/openmp/trunk/runtime/src/kmp_tasking.c?rev=266675&r1=266674&r2=266675&view=diff
==============================================================================
--- openmp/trunk/runtime/src/kmp_tasking.c (original)
+++ openmp/trunk/runtime/src/kmp_tasking.c Mon Apr 18 16:35:14 2016
@@ -284,6 +284,13 @@ __kmp_push_task(kmp_int32 gtid, kmp_task
 
     KA_TRACE(20, ("__kmp_push_task: T#%d trying to push task %p.\n", gtid, taskdata ) );
 
+    if ( taskdata->td_flags.tiedness == TASK_UNTIED ) {
+        // untied task needs to increment counter so that the task structure is not freed prematurely
+        kmp_int32 counter = 1 + KMP_TEST_THEN_INC32(&taskdata->td_untied_count);
+        KA_TRACE(20, ( "__kmp_push_task: T#%d untied_count (%d) incremented for task %p\n",
+                       gtid, counter, taskdata ) );
+    }
+
     // The first check avoids building task_team thread data if serialized
     if ( taskdata->td_flags.task_serial ) {
         KA_TRACE(20, ( "__kmp_push_task: T#%d team serialized; returning TASK_NOT_PUSHED for task %p\n",
@@ -436,8 +443,8 @@ __kmp_task_start( kmp_int32 gtid, kmp_ta
     // mark starting task as executing and as current task
     thread -> th.th_current_task = taskdata;
 
-    KMP_DEBUG_ASSERT( taskdata -> td_flags.started == 0 );
-    KMP_DEBUG_ASSERT( taskdata -> td_flags.executing == 0 );
+    KMP_DEBUG_ASSERT( taskdata->td_flags.started == 0 || taskdata->td_flags.tiedness == TASK_UNTIED );
+    KMP_DEBUG_ASSERT( taskdata->td_flags.executing == 0 || taskdata->td_flags.tiedness == TASK_UNTIED );
     taskdata -> td_flags.started = 1;
     taskdata -> td_flags.executing = 1;
     KMP_DEBUG_ASSERT( taskdata -> td_flags.complete == 0 );
@@ -498,6 +505,13 @@ __kmpc_omp_task_begin_if0( ident_t *loc_
     KA_TRACE(10, ("__kmpc_omp_task_begin_if0(enter): T#%d loc=%p task=%p current_task=%p\n",
                   gtid, loc_ref, taskdata, current_task ) );
 
+    if ( taskdata->td_flags.tiedness == TASK_UNTIED ) {
+        // untied task needs to increment counter so that the task structure is not freed prematurely
+        kmp_int32 counter = 1 + KMP_TEST_THEN_INC32(&taskdata->td_untied_count);
+        KA_TRACE(20, ( "__kmpc_omp_task_begin_if0: T#%d untied_count (%d) incremented for task %p\n",
+                       gtid, counter, taskdata ) );
+    }
+
     taskdata -> td_flags.task_serial = 1;  // Execute this task immediately, not deferred.
     __kmp_task_start( gtid, task, current_task );
 
@@ -646,6 +660,25 @@ __kmp_task_finish( kmp_int32 gtid, kmp_t
     }
 #endif /* BUILD_TIED_TASK_STACK */
 
+    if ( taskdata->td_flags.tiedness == TASK_UNTIED ) {
+        // untied task needs to check the counter so that the task structure is not freed prematurely
+        kmp_int32 counter = KMP_TEST_THEN_DEC32(&taskdata->td_untied_count) - 1;
+        KA_TRACE(20, ( "__kmp_task_finish: T#%d untied_count (%d) decremented for task %p\n",
+                       gtid, counter, taskdata ) );
+        if ( counter > 0 ) {
+            // untied task is not done, to be continued possibly by other thread, do not free it now
+            if (resumed_task == NULL) {
+                KMP_DEBUG_ASSERT( taskdata->td_flags.task_serial );
+                resumed_task = taskdata->td_parent;  // In a serialized task, the resumed task is the parent
+            }
+            thread->th.th_current_task = resumed_task; // restore current_task
+            resumed_task->td_flags.executing = 1;  // resume previous task
+            KA_TRACE(10, ("__kmp_task_finish(exit): T#%d partially done task %p, resuming task %p\n",
+                          gtid, taskdata, resumed_task) );
+            return;
+        }
+    }
+
     KMP_DEBUG_ASSERT( taskdata -> td_flags.complete == 0 );
     taskdata -> td_flags.complete = 1;   // mark the task as completed
     KMP_DEBUG_ASSERT( taskdata -> td_flags.started == 1 );
@@ -980,6 +1013,7 @@ __kmp_task_alloc( ident_t *loc_ref, kmp_
     taskdata->td_alloc_thread = thread;
     taskdata->td_parent       = parent_task;
     taskdata->td_level        = parent_task->td_level + 1; // increment nesting level
+    taskdata->td_untied_count = 0;
     taskdata->td_ident        = loc_ref;
     taskdata->td_taskwait_ident   = NULL;
     taskdata->td_taskwait_counter = 0;