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Re: [PATCH 6/6, OpenACC, libgomp] Async re-work, nvptx changes (revised, v3)


On 2018/12/11 9:50 PM, Chung-Lin Tang wrote:
On 2018/12/10 6:02 PM, Chung-Lin Tang wrote:
On 2018/12/7 04:57 AM, Thomas Schwinge wrote>> --- 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?)

IIUC, this non-blocking only pertains to the "Legacy Default Stream" in CUDA, which we're pretty much ignoring; we should be using the newer per-thread default stream model. We could review this issue later.

+  if (aq->cuda_stream == NULL)
+    GOMP_PLUGIN_fatal ("CUDA stream create NULL\n");

Can this actually happen, given the "CUDA_CALL_ASSERT" usage above?

Hmm, yeah I think this is superfluous too...

+  CUDA_CALL_ASSERT (cuStreamSynchronize, aq->cuda_stream);

Why is the synchronization needed here?

I don't remember, could likely be something added during debug.
I'll remove this and test if things are okay.

I have removed the above seemingly unneeded lines and re-tested, appears okay.
Also the formerly attached version seemed to for some reason had many conflicts
with older code, all resolved in this v2 nvptx part.

GOMP_OFFLOAD_openacc_async_construct is updated to return NULL for failure,
there's also some adjustments in oacc-async.c, coming next.

Chung-Lin



Attachment: 06.nvptx.v2-v3.diff
Description: Text document

Attachment: async-06.nvptx.v3.patch
Description: Text document


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