[committed,nvptx,libgomp] Don't launch with num_workers == 0

Message ID 20190109001004.GA29783@delia
State New
Headers show
Series
  • [committed,nvptx,libgomp] Don't launch with num_workers == 0
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Commit Message

Tom de Vries Jan. 9, 2019, 12:10 a.m.
Hi,

When using a compiler build with:
...
+#define PTX_DEFAULT_VECTOR_LENGTH PTX_CTA_SIZE
+#define PTX_MAX_VECTOR_LENGTH PTX_CTA_SIZE
...
and running the libgomp testsuite, we run into an execution failure in
parallel-loop-1.c, due to a cuda launch failure:
...
  nvptx_exec: kernel f6_none_none$_omp_fn$0: launch gangs=480, workers=0, \
    vectors=1024

libgomp: cuLaunchKernel error: invalid argument
...
because workers == 0.

The workers variable is set to 0 here in nvptx_exec:
...
                workers = blocks / actual_vectors;
...
because actual_vectors is 1024, and blocks is 768:
...
cuOccupancyMaxPotentialBlockSize: grid = 10, block = 768
...

Fix this by ensuring that workers is at least one.

Committed to trunk.

Thanks,
- Tom

[nvptx, libgomp] Don't launch with num_workers == 0

2019-01-08  Tom de Vries  <tdevries@suse.de>

	* plugin/plugin-nvptx.c (nvptx_exec): Make sure to launch with at least
	one worker.

---
 libgomp/plugin/plugin-nvptx.c | 1 +
 1 file changed, 1 insertion(+)

Patch

diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index 572d9ef8d5c..60553bdf3bd 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -1272,6 +1272,7 @@  nvptx_exec (void (*fn), size_t mapnum, void **hostaddrs, void **devaddrs,
 				      ? vectors
 				      : dims[GOMP_DIM_VECTOR]);
 		workers = blocks / actual_vectors;
+		workers = MAX (workers, 1);
 	      }
 
 	    for (i = 0; i != GOMP_DIM_MAX; i++)