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Re: [PATCH 6/6, OpenACC, libgomp] Async re-work, nvptx changes
- From: Thomas Schwinge <thomas at codesourcery dot com>
- To: Chung-Lin Tang <cltang at codesourcery dot com>
- Cc: <gcc-patches at gcc dot gnu dot org>, Tom de Vries <tdevries at suse dot de>
- Date: Thu, 6 Dec 2018 21:57:33 +0100
- Subject: Re: [PATCH 6/6, OpenACC, libgomp] Async re-work, nvptx changes
- References: <firstname.lastname@example.org>
On Tue, 25 Sep 2018 21:11:58 +0800, Chung-Lin Tang <email@example.com> wrote:
> Hi Tom,
> this patch removes large portions of plugin/plugin-nvptx.c, since a lot of it is
> now in oacc-async.c now. The new code is essentially a NVPTX/CUDA-specific implementation
> of the new-style goacc_asyncqueues.
> --- a/libgomp/plugin/plugin-nvptx.c
> +++ b/libgomp/plugin/plugin-nvptx.c
> +struct goacc_asyncqueue *
> +GOMP_OFFLOAD_openacc_async_construct (void)
> + struct goacc_asyncqueue *aq
> + = GOMP_PLUGIN_malloc (sizeof (struct goacc_asyncqueue));
> + aq->cuda_stream = NULL;
> + CUDA_CALL_ASSERT (cuStreamCreate, &aq->cuda_stream, CU_STREAM_DEFAULT);
Curiously (this was the same in the code before): does this have to be
"CU_STREAM_DEFAULT" instead of "CU_STREAM_NON_BLOCKING", because we want
to block anything from running in parallel with "acc_async_sync" GPU
kernels, that use the "NULL" stream? (Not asking you to change this now,
but I wonder if this is overly strict?)
> + if (aq->cuda_stream == NULL)
> + GOMP_PLUGIN_fatal ("CUDA stream create NULL\n");
Can this actually happen, given the "CUDA_CALL_ASSERT" usage above?
> + CUDA_CALL_ASSERT (cuStreamSynchronize, aq->cuda_stream);
Why is the synchronization needed here?
> + return aq;