Hi,
atm parallel-dims.c fails on Titan-V, with a cuda launch failure:
...
libgomp: cuLaunchKernel error: too many resources requested for launch
...
We've got a check in the libgomp nvptx plugin to prevent the cuda launch
failure and give a more informative error message:
...
/* Check if the accelerator has sufficient hardware resources to
launch the offloaded kernel. */
if (dims[GOMP_DIM_WORKER] > 1)
{
if (reg_granularity > 0
&& dims[GOMP_DIM_WORKER] > threads_per_block)
GOMP_PLUGIN_fatal
("The Nvidia accelerator has insufficient resources "
"to launch '%s'; recompile the program with "
"'num_workers = %d' on that offloaded region or "
"'-fopenacc-dim=-:%d'.\n",
targ_fn->launch->fn, threads_per_block,
threads_per_block);
}
...
The message doesn't trigger, because reg_granularity == -1.
This value comes from dev->register_allocation_granularity which
defaults to -1 because libgomp does not have a hardcoded constant for
sm_70. The hardcoded constants that are present match 'Warp Allocation
Granularity' in the GPU Data table in CUDA_Occupancy_calculator.xls, but
AFAICT there's no column published yet for sm_70.
Furthermore, the comparison to threads_per_block is not correct. What we
want here is the maximum amount of threads per block, while the
threads_per_block variable contains an approximation of that, and the
exact amount required is already available from the CUDA runtime and
stored at targ_fn->max_threads_per_block.
Then, the comparison to dims[GOMP_DIM_WORKER] is incorrect. It used to
be correct before "[nvptx] Handle large vectors in libgomp" when we used
to do "threads_per_block /= warp_size", but now we need to compare
against dims[GOMP_DIM_WORKER] * dims[GOMP_DIM_VECTOR].
Finally, the message has not been updated to reflect that vector length
can be larger than 32.
The patch addresses these issues.
Committed to og7.
Thanks,
- Tom
[libgomp, nvptx] Fix too-many-resources fatal error condition and message
2018-04-30 Tom de Vries <t...@codesourcery.com>
* plugin/plugin-nvptx.c (nvptx_exec): Fix
insufficient-resources-to-launch fatal error condition and message.
---
libgomp/plugin/plugin-nvptx.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)
diff --git a/libgomp/plugin/plugin-nvptx.c b/libgomp/plugin/plugin-nvptx.c
index 9b4768f..3c00555 100644
--- a/libgomp/plugin/plugin-nvptx.c
+++ b/libgomp/plugin/plugin-nvptx.c
@@ -834,16 +834,15 @@ nvptx_exec (void (*fn), size_t mapnum, void **hostaddrs, void **devaddrs,
/* Check if the accelerator has sufficient hardware resources to
launch the offloaded kernel. */
- if (dims[GOMP_DIM_WORKER] > 1)
- {
- if (reg_granularity > 0 && dims[GOMP_DIM_WORKER] > threads_per_block)
- GOMP_PLUGIN_fatal ("The Nvidia accelerator has insufficient resources "
- "to launch '%s'; recompile the program with "
- "'num_workers = %d' on that offloaded region or "
- "'-fopenacc-dim=-:%d'.\n",
- targ_fn->launch->fn, threads_per_block,
- threads_per_block);
- }
+ if (dims[GOMP_DIM_WORKER] * dims[GOMP_DIM_VECTOR]
+ > targ_fn->max_threads_per_block)
+ GOMP_PLUGIN_fatal ("The Nvidia accelerator has insufficient resources to"
+ " launch '%s' with num_workers = %d and vector_length ="
+ " %d; recompile the program with 'num_workers = x and"
+ " vector_length = y' on that offloaded region or "
+ "'-fopenacc-dim=-:x:y' where x * y <= %d.\n",
+ targ_fn->launch->fn, dims[GOMP_DIM_WORKER],
+ dims[GOMP_DIM_VECTOR], targ_fn->max_threads_per_block);
GOMP_PLUGIN_debug (0, " %s: kernel %s: launch"
" gangs=%u, workers=%u, vectors=%u\n",
