Re: [PATCH 2/6, OpenACC, libgomp] Async re-work, oacc-* parts (revised, v2)

[Thomas Schwinge <thomas at codesourcery dot com>]

Hi Chung-Lin!

On Tue, 18 Dec 2018 23:06:38 +0800, Chung-Lin Tang <chunglin_tang@mentor.com> wrote:
> this part includes some of the lookup_goacc_asyncqueue fixes we talked about.
> I am still thinking about how the queue lock problem should really be solved, so regard
> this patch as just fixing some of the problems.

Sure, thanks.

Two comments, though:

> --- libgomp/oacc-async.c	(revision 267226)
> +++ libgomp/oacc-async.c	(working copy)

> +attribute_hidden struct goacc_asyncqueue *
> +lookup_goacc_asyncqueue (struct goacc_thread *thr, bool create, int async)
> +{
> +  /* The special value acc_async_noval (-1) maps to the thread-specific
> +     default async stream.  */
> +  if (async == acc_async_noval)
> +    async = thr->default_async;
> +
> +  if (async == acc_async_sync)
> +    return NULL;
> +
> +  if (async < 0)
> +    gomp_fatal ("bad async %d", async);
> +
> +  struct gomp_device_descr *dev = thr->dev;
> +
> +  gomp_mutex_lock (&dev->openacc.async.lock);
> +
> +  if (!create
> +      && (async >= dev->openacc.async.nasyncqueue
> +	  || !dev->openacc.async.asyncqueue[async]))
> +    {
> +      gomp_mutex_unlock (&dev->openacc.async.lock);
> +      return NULL;
> +    }
> +
> +  if (async >= dev->openacc.async.nasyncqueue)
> +    {
> +      int diff = async + 1 - dev->openacc.async.nasyncqueue;
> +      dev->openacc.async.asyncqueue
> +	= gomp_realloc (dev->openacc.async.asyncqueue,
> +			sizeof (goacc_aq) * (async + 1));
> +      memset (dev->openacc.async.asyncqueue + dev->openacc.async.nasyncqueue,
> +	      0, sizeof (goacc_aq) * diff);
> +      dev->openacc.async.nasyncqueue = async + 1;
> +    }
> +
> +  if (!dev->openacc.async.asyncqueue[async])
> +    {
> +      dev->openacc.async.asyncqueue[async] = dev->openacc.async.construct_func ();
> +
> +      if (!dev->openacc.async.asyncqueue[async])
> +	{
> +	  gomp_mutex_unlock (&dev->openacc.async.lock);
> +	  gomp_fatal ("async %d creation failed", async);
> +	}

That will now always fail for host fallback, where
"host_openacc_async_construct" just always does "return NULL".

Actually, if the device doesn't support asyncqueues, this whole function
should turn into some kind of no-op, so that we don't again and again try
to create a new one for every call to "lookup_goacc_asyncqueue".

I'm attaching one possible solution.  I think it's fine to assume that
the majority of devices will support asyncqueues, and for those that
don't, this is just a one-time overhead per async-argument.  So, no
special handling required in "lookup_goacc_asyncqueue".

> +      /* Link new async queue into active list.  */
> +      goacc_aq_list n = gomp_malloc (sizeof (struct goacc_asyncqueue_list));
> +      n->aq = dev->openacc.async.asyncqueue[async];
> +      n->next = dev->openacc.async.active;
> +      dev->openacc.async.active = n;
> +    }
> +  gomp_mutex_unlock (&dev->openacc.async.lock);

You still need to keep "async" locked during...

> +  return dev->openacc.async.asyncqueue[async];

... this dereference.

> +}


Oh, and:

> --- libgomp/oacc-plugin.c	(revision 267226)
> +++ libgomp/oacc-plugin.c	(working copy)
> @@ -31,14 +31,10 @@
>  #include "oacc-int.h"
>  
>  void
> -GOMP_PLUGIN_async_unmap_vars (void *ptr, int async)
> +GOMP_PLUGIN_async_unmap_vars (void *ptr __attribute__((unused)),
> +			      int async __attribute__((unused)))
>  {
> -  struct target_mem_desc *tgt = ptr;
> -  struct gomp_device_descr *devicep = tgt->device_descr;
> -
> -  devicep->openacc.async_set_async_func (async);
> -  gomp_unmap_vars (tgt, true);
> -  devicep->openacc.async_set_async_func (acc_async_sync);
> +  gomp_fatal ("invalid plugin function");
>  }

Please add a comment here, something like: "Obsolete entry point, no
longer used."


Grüße
 Thomas


>From 4cb99c3691f95b6b299e7cb2603af36f723f9e8e Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Tue, 18 Dec 2018 21:58:41 +0100
Subject: [PATCH] into async re-work: adjust host_openacc_async_construct

---
 libgomp/oacc-host.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libgomp/oacc-host.c b/libgomp/oacc-host.c
index 727f8866f45c..cfd8a24f0674 100644
--- a/libgomp/oacc-host.c
+++ b/libgomp/oacc-host.c
@@ -212,7 +212,8 @@ host_openacc_async_queue_callback (struct goacc_asyncqueue *aq
 static struct goacc_asyncqueue *
 host_openacc_async_construct (void)
 {
-  return NULL;
+  /* We have to return non-NULL here, but it's OK to use a dummy.  */
+  return (struct goacc_asyncqueue *) -1;
 }
 
 static bool
-- 
2.17.1