Allow parallel OpenMP workers to be viewed as sequential ones for specific tasks, then rebind automatically.

examples/sched_ctx/parallel_tasks_with_cluster_api.c

@@ -101,7 +101,14 @@ int main(int argc, char **argv)
 				    STARPU_VALUE,&size,sizeof(int),
 				    0);
 		t->destroy = 1;
-		t->possibly_parallel = 1;
+		/* For two tasks, try out the case when the task isn't parallel and expect
+			 the configuration to be sequential due to this, then automatically changed
+			 back to the parallel one */
+		if (i<=4 || i > 6)
+			t->possibly_parallel = 1;
+		/* Note that this mode requires that you put a prologue callback managing
+			 this on all tasks to be taken into account. */
+		t->prologue_callback_pop_func = &starpu_openmp_prologue;
 
 		ret=starpu_task_submit(t);
 		if (ret == -ENODEV)

include/starpu_clusters_util.h

@@ -72,10 +72,10 @@ int starpu_uncluster_machine(struct starpu_cluster_machine* clusters);
 int starpu_cluster_print(struct starpu_cluster_machine* clusters);
 
 /* Prologue functions */
-void starpu_openmp_prologue(void * sched_ctx_id);
+void starpu_openmp_prologue(void*);
 #define starpu_intel_openmp_mkl_prologue starpu_openmp_prologue
 #ifdef STARPU_MKL
-void starpu_gnu_openmp_mkl_prologue(void * sched_ctx_id);
+void starpu_gnu_openmp_mkl_prologue(void*);
 #endif /* STARPU_MKL */
 
 #ifdef __cplusplus

src/core/sched_ctx.c

@@ -566,6 +566,7 @@ struct _starpu_sched_ctx* _starpu_create_sched_ctx(struct starpu_sched_policy *p
 		sched_ctx->sleeping[w] = 0;
 	}
 
+	sched_ctx->parallel_view = 0;
 
         /*init the strategy structs and the worker_collection of the ressources of the context */
 	if(policy)

src/core/sched_ctx.h

@@ -168,6 +168,10 @@ struct _starpu_sched_ctx
 	/* perf model for the device comb of the ctx */
 	struct starpu_perfmodel_arch perf_arch;
 
+	/* For parallel workers, say whether it is viewed as sequential or not. This
+		 is a helper for the prologue code. */
+	unsigned parallel_view;
+
 	/* for ctxs without policy: flag to indicate that we want to get
 	   the threads to sleep in order to replace them with other threads or leave
 	   them awake & use them in the parallel code*/

src/core/sched_policy.c

@@ -989,7 +989,11 @@ profiling:
 	}
 
 	if(task->prologue_callback_pop_func)
+	{
+		_starpu_set_current_task(task);
 		task->prologue_callback_pop_func(task->prologue_callback_pop_arg);
+		_starpu_set_current_task(NULL);
+	}
 
 	return task;
 }

src/util/starpu_clusters_create.c

@@ -45,45 +45,67 @@ starpu_binding_function _starpu_cluster_type_get_func(starpu_cluster_types type)
 	return prologue_func;
 }
 
-void starpu_openmp_prologue(void *sched_ctx_id)
+void starpu_openmp_prologue(void* arg)
 {
-	int sched_ctx = *(int*)sched_ctx_id;
-	int *cpuids = NULL;
-	int ncpuids = 0;
 	int workerid = starpu_worker_get_id_check();
 
 	if (starpu_worker_get_type(workerid) == STARPU_CPU_WORKER)
 	{
-		starpu_sched_ctx_get_available_cpuids(sched_ctx, &cpuids, &ncpuids);
-		omp_set_num_threads(ncpuids);
-#pragma omp parallel
+		struct starpu_task *task = starpu_task_get_current();
+		int sched_ctx = task->sched_ctx;
+		struct _starpu_sched_ctx *ctx_struct = _starpu_get_sched_ctx_struct(sched_ctx);
+		/* If the view of the worker doesn't correspond to the view of the task,
+			 adapt the thread team */
+		if (ctx_struct->parallel_view != task->possibly_parallel)
 		{
-			starpu_sched_ctx_bind_current_thread_to_cpuid(cpuids[omp_get_thread_num()]);
+			int *cpuids = NULL;
+			int ncpuids = 0;
+
+			starpu_sched_ctx_get_available_cpuids(sched_ctx, &cpuids, &ncpuids);
+			if (!task->possibly_parallel)
+				ncpuids=1;
+			omp_set_num_threads(ncpuids);
+#pragma omp parallel
+			{
+				starpu_sched_ctx_bind_current_thread_to_cpuid(cpuids[omp_get_thread_num()]);
+			}
+			free(cpuids);
+			ctx_struct->parallel_view = !ctx_struct->parallel_view;
 		}
-		free(cpuids);
 	}
 	return;
 }
 
 #ifdef STARPU_MKL
-void starpu_gnu_openmp_mkl_prologue(void *sched_ctx_id)
+void starpu_gnu_openmp_mkl_prologue(void* arg)
 {
-	int sched_ctx = *(int*)sched_ctx_id;
-	int *cpuids = NULL;
-	int ncpuids = 0;
 	int workerid = starpu_worker_get_id();
 
 	if (starpu_worker_get_type(workerid) == STARPU_CPU_WORKER)
 	{
-		starpu_sched_ctx_get_available_cpuids(sched_ctx, &cpuids, &ncpuids);
-		omp_set_num_threads(ncpuids);
-		mkl_set_num_threads(ncpuids);
-		mkl_set_dynamic(0);
-#pragma omp parallel
+		struct starpu_task *task = starpu_task_get_current();
+		int sched_ctx = task->sched_ctx;
+		struct _starpu_sched_ctx *ctx_struct = _starpu_get_sched_ctx_struct(sched_ctx);
+		/* If the view of the worker doesn't correspond to the view of the task,
+			 adapt the thread team */
+		if (ctx_struct->parallel_view != task->possibly_parallel)
 		{
-			starpu_sched_ctx_bind_current_thread_to_cpuid(cpuids[omp_get_thread_num()]);
+			int *cpuids = NULL;
+			int ncpuids = 0;
+
+			starpu_sched_ctx_get_available_cpuids(sched_ctx, &cpuids, &ncpuids);
+			if (!task->possibly_parallel)
+				ncpuids=1;
+			omp_set_num_threads(ncpuids);
+			mkl_set_num_threads(ncpuids);
+			mkl_set_dynamic(0);
+#pragma omp parallel
+			{
+				starpu_sched_ctx_bind_current_thread_to_cpuid(cpuids[omp_get_thread_num()]);
+			}
+			free(cpuids);
+			ctx_struct->parallel_view = !ctx_struct->parallel_view;
 		}
-		free(cpuids);
 	}
 	return;
 }
@@ -324,8 +346,8 @@ int _starpu_cluster_bind(struct _starpu_cluster *cluster)
 	else
 	{
 		func = _starpu_cluster_type_get_func(cluster->params->type);
-		func_arg = (void*) &cluster->id;
-		}
+		func_arg = NULL;
+	}
 
 	return starpu_task_insert(&_starpu_cluster_bind_cl,
 				  STARPU_SCHED_CTX, cluster->id,