Move BACKOFF_{MIN,MAX} constants to execution env vars

ChangeLog

@@ -57,6 +57,9 @@ Small features:
   * Add field starpu_conf::precedence_over_environment_variables to ignore
     environment variables when parameters are set directly in starpu_conf
   * Add starpu_data_get_coordinates_array
+  * New STARPU_BACKOFF_MIN and STARPU_BACKOFF_MAX environment variables to the
+    exponential backoff limits of the number of cycles to pause while drivers
+    are spinning.
 
 StarPU 1.3.3 (git revision 11afc5b007fe1ab1c729b55b47a5a98ef7f3cfad)
 ====================================================================

doc/doxygen/chapters/501_environment_variables.doxy

@@ -406,6 +406,20 @@ and friends.  The default is Enabled.
 This permits to test the performance effect of memory pinning.
 </dd>
 
+<dt>STARPU_BACKOFF_MIN</dt>
+<dd>
+\anchor STARPU_BACKOFF_MIN
+\addindex __env__STARPU_BACKOFF_MIN
+Set minimum exponential backoff of number of cycles to pause when spinning. Default value is 1.
+</dd>
+
+<dt>STARPU_BACKOFF_MAX</dt>
+<dd>
+\anchor STARPU_BACKOFF_MAX
+\addindex __env__STARPU_BACKOFF_MAX
+Set maximum exponential backoff of number of cycles to pause when spinning. Default value is 32.
+</dd>
+
 <dt>STARPU_MIC_SINK_PROGRAM_NAME</dt>
 <dd>
 \anchor STARPU_MIC_SINK_PROGRAM_NAME

include/starpu.h

@@ -441,6 +441,16 @@ struct starpu_conf
 	   performance counters after initialization
 	 */
 	unsigned start_perf_counter_collection;
+
+	/**
+	   Minimum spinning backoff of drivers. Default value: \c 1
+	 */
+	unsigned driver_spinning_backoff_min;
+
+	/**
+	   Maximum spinning backoff of drivers. Default value: \c 32
+	 */
+	unsigned driver_spinning_backoff_max;
 };
 
 /**

src/core/workers.c

@@ -1143,6 +1143,9 @@ int starpu_conf_init(struct starpu_conf *conf)
 	/* 64MiB by default */
 	conf->trace_buffer_size = ((uint64_t) starpu_get_env_number_default("STARPU_TRACE_BUFFER_SIZE", 64)) << 20;
 
+	conf->driver_spinning_backoff_min = (unsigned) starpu_get_env_number_default("STARPU_BACKOFF_MIN", 1);
+	conf->driver_spinning_backoff_max = (unsigned) starpu_get_env_number_default("STARPU_BACKOFF_MAX", 32);
+
 	/* Do not start performance counter collection by default */
 	conf->start_perf_counter_collection = 0;
 	return 0;

src/drivers/driver_common/driver_common.c

@@ -28,8 +28,6 @@
 #include <core/debug.h>
 #include <core/task.h>
 
-#define BACKOFF_MAX 32  /* TODO : use parameter to define them */
-#define BACKOFF_MIN 1
 
 void _starpu_driver_start_job(struct _starpu_worker *worker, struct _starpu_job *j, struct starpu_perfmodel_arch* perf_arch, int rank, int profiling)
 {
@@ -374,7 +372,7 @@ static void _starpu_exponential_backoff(struct _starpu_worker *worker)
 {
 	int delay = worker->spinning_backoff;
 
-	if (worker->spinning_backoff < BACKOFF_MAX)
+	if (worker->spinning_backoff < worker->config->conf.driver_spinning_backoff_max)
 		worker->spinning_backoff<<=1;
 
 	while(delay--)
@@ -504,7 +502,7 @@ struct starpu_task *_starpu_get_worker_task(struct _starpu_worker *worker, int w
 	{
 		_starpu_worker_set_status_sleeping(workerid);
 	}
-	worker->spinning_backoff = BACKOFF_MIN;
+	worker->spinning_backoff = worker->config->conf.driver_spinning_backoff_min;
 
 	_starpu_worker_leave_sched_op(worker);
 	STARPU_PTHREAD_COND_BROADCAST(&worker->sched_cond);
@@ -703,7 +701,7 @@ int _starpu_get_multi_worker_task(struct _starpu_worker *workers, struct starpu_
 	}
 
 	_starpu_worker_set_status_wakeup(workerid);
-	worker->spinning_backoff = BACKOFF_MIN;
+	worker->spinning_backoff = worker->config->conf.driver_spinning_backoff_min;
 #endif /* !STARPU_SIMGRID */
 
 	_starpu_worker_leave_sched_op(&workers[0]);