Fix documentation and assert for STARPU_CUDA_THREAD_PER_WORKER and STARPU_CUDA_THREAD_PER_DEV

doc/doxygen/chapters/501_environment_variables.doxy

@@ -2,7 +2,7 @@
  *
  * Copyright (C) 2011-2013,2015-2017                      Inria
  * Copyright (C) 2010-2018                                CNRS
- * Copyright (C) 2009-2011,2013-2017                      Université de Bordeaux
+ * Copyright (C) 2009-2011,2013-2018                      Université de Bordeaux
  * Copyright (C) 2016                                     Uppsala University
  *
  * StarPU is free software; you can redistribute it and/or modify
@@ -66,19 +66,21 @@ which will be concurrently running on the devices. The default value is 1.
 <dd>
 \anchor STARPU_CUDA_THREAD_PER_WORKER
 \addindex __env__STARPU_CUDA_THREAD_PER_WORKER
-Specify if the cuda driver should provide a thread per stream or a single thread
-dealing with all the streams. 0 if one thread per stream, 1 otherwise. The default
-value is 0. Setting it to 1 is contradictory with setting STARPU_CUDA_THREAD_PER_DEV to 1.
+Specify whether the cuda driver should use one thread per stream (1) or to use
+a single thread to drive all the streams of the device or all devices (0), and
+STARPU_CUDA_THREAD_PER_DEV determines whether is it one thread per device or one
+thread for all devices. The default value is 0. Setting it to 1 is contradictory
+with setting STARPU_CUDA_THREAD_PER_DEV.
 </dd>
 
 <dt>STARPU_CUDA_THREAD_PER_DEV</dt>
 <dd>
 \anchor STARPU_CUDA_THREAD_PER_DEV
 \addindex __env__STARPU_CUDA_THREAD_PER_DEV
-Specify if the cuda driver should provide a thread per device or a single thread
-dealing with all the devices. 0 if one thread per device, 1 otherwise. The default
-value is 1, unless STARPU_CUDA_THREAD_PER_WORKER is set to 1. Setting it to 1 is
-contradictory with setting STARPU_CUDA_THREAD_PER_WORKER to 1.
+Specify whether the cuda driver should use one thread per device (1) or to use a
+single thread to drive all the devices (0). The default value is 1.  It does not
+make sense to set this variable if STARPU_CUDA_THREAD_PER_WORKER is set to to 1
+(since STARPU_CUDA_THREAD_PER_DEV is then meaningless).
 </dd>
 
 <dt>STARPU_CUDA_PIPELINE</dt>

src/core/topology.c

@@ -1437,6 +1437,8 @@ _starpu_init_machine_config(struct _starpu_machine_config *config, int no_mp_con
 	topology->cuda_th_per_stream = starpu_get_env_number_default("STARPU_CUDA_THREAD_PER_WORKER", -1);
 	topology->cuda_th_per_dev = starpu_get_env_number_default("STARPU_CUDA_THREAD_PER_DEV", -1);
 
+	STARPU_ASSERT_MSG(!(topology->cuda_th_per_stream == 1 && topology->cuda_th_per_dev != -1), "It does not make sense to set both STARPU_CUDA_THREAD_PER_WORKER to 1 and to set STARPU_CUDA_THREAD_PER_DEV, please choose either per worker or per device or none");
+
 	/* per device by default */
 	if (topology->cuda_th_per_dev == -1)
 	{
@@ -1451,8 +1453,6 @@ _starpu_init_machine_config(struct _starpu_machine_config *config, int no_mp_con
 		topology->cuda_th_per_stream = 0;
 	}
 
-	STARPU_ASSERT_MSG(topology->cuda_th_per_dev != 1 || topology->cuda_th_per_stream != 1, "It does not make sense to set both STARPU_CUDA_THREAD_PER_WORKER and STARPU_CUDA_THREAD_PER_DEV to 1, please choose either per worker or per device or none");
-
 	if (!topology->cuda_th_per_dev)
 	{
 		cuda_worker_set[0].workers = &config->workers[topology->nworkers];