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From: Alexander Monakov <amonakov@ispras.ru>
To: Tobias Burnus <tobias@codesourcery.com>
Cc: Jakub Jelinek <jakub@redhat.com>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [Patch][v5] libgomp/nvptx: Prepare for reverse-offload callback handling
Date: Wed, 19 Oct 2022 18:53:47 +0300 (MSK)	[thread overview]
Message-ID: <c1404b7-60b6-b4cb-b1d-ca47a0ecc4ff@ispras.ru> (raw)
In-Reply-To: <1e56b27f-3c74-8bc2-028b-9091fa1ae7b1@codesourcery.com>

[-- Attachment #1: Type: text/plain, Size: 2056 bytes --]

On Wed, 12 Oct 2022, Tobias Burnus wrote:

> On 11.10.22 13:12, Alexander Monakov wrote:
> > My understanding is such trickery should not be necessary with
> > the barrier-based approach, i.e. the sequence of PTX instructions
> >
> >    st   % plain store
> >    membar.sys
> >    st.volatile
> >
> > should be enough to guarantee that the former store is visible on the host
> > before the latter, and work all the way back to sm_20.
> 
> If I understand it correctly, you mean:
> 
>   GOMP_REV_OFFLOAD_VAR->dev_num = GOMP_ADDITIONAL_ICVS.device_num;
> 
>   __sync_synchronize ();  /* membar.sys */
>   asm volatile ("st.volatile.global.u64 [%0], %1;"
>                 : : "r"(addr_struct_fn), "r" (fn) : "memory");
> 
> 
> And then directly followed by the busy wait:
> 
>   while (__atomic_load_n (&GOMP_REV_OFFLOAD_VAR->fn, __ATOMIC_ACQUIRE) != 0)
>     ;  /* spin  */
> 
> which GCC expands to:
> 
>   /* ld.global.u64 %r64,[__gomp_rev_offload_var];
>      ld.u64 %r36,[%r64];
>      membar.sys;  */
> 
> The such updated patch is attached.

I think the topic for which I was Cc'ed (memory space and access method for
the synchronization variable) has been resolved nicely. I am not satisfied
with some other points raised in the conversation, I hope they are noted.

Alexander

> (This is the only change + removing the mkoffload.cc part is the only
> larger change. Otherwise, it only handles the minor comments by Jakub.
> The now removed CU_DEVICE_ATTRIBUTE_ASYNC_ENGINE_COUNT was used
> until commit r10-304-g1f4c5b9bb2eb81880e2bc725435d596fcd2bdfef i.e.
> it is a really old left over!)
> 
> Otherwise, tested* to work with sm_30 (error by mkoffload, unchanged),
> sm_35 and sm_70.
> 
> Tobias
> 
> *With some added code; until GOMP_OFFLOAD_get_num_devices accepts
> GOMP_REQUIRES_UNIFIED_SHARED_MEMORY and GOMP_OFFLOAD_load_image
> gets passed a non-NULL for rev_fn_table, the current patch is a no op.
> 
> Planned next is the related GCN patch – and the actual change
> in libgomp/target.c (+ accepting USM in GOMP_OFFLOAD_get_num_devices)

  parent reply	other threads:[~2022-10-19 15:53 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-26  9:07 [Patch] " Tobias Burnus
2022-08-26  9:07 ` Tobias Burnus
2022-08-26 14:56 ` Alexander Monakov
2022-09-09 15:49   ` Jakub Jelinek
2022-09-09 15:51 ` Jakub Jelinek
2022-09-13  7:07 ` Tobias Burnus
2022-09-21 20:06   ` Alexander Monakov
2022-09-26 15:07     ` Tobias Burnus
2022-09-26 17:45       ` Alexander Monakov
2022-09-27  9:23         ` Tobias Burnus
2022-09-28 13:16           ` Alexander Monakov
2022-10-02 18:13           ` Tobias Burnus
2022-10-07 14:26             ` [Patch][v5] " Tobias Burnus
2022-10-11 10:49               ` Jakub Jelinek
2022-10-11 11:12                 ` Alexander Monakov
2022-10-12  8:55                   ` Tobias Burnus
2022-10-17  7:35                     ` *ping* / " Tobias Burnus
2022-10-19 15:53                     ` Alexander Monakov [this message]
2022-10-24 14:07                     ` Jakub Jelinek
2022-10-24 19:05                       ` Thomas Schwinge
2022-10-24 19:11                         ` Thomas Schwinge
2022-10-24 19:46                           ` Tobias Burnus
2022-10-24 19:51                           ` libgomp/nvptx: Prepare for reverse-offload callback handling, resolve spurious SIGSEGVs (was: [Patch][v5] libgomp/nvptx: Prepare for reverse-offload callback handling) Thomas Schwinge
2023-03-21 15:53 ` libgomp: Simplify OpenMP reverse offload host <-> device memory copy implementation (was: [Patch] " Thomas Schwinge
2023-03-24 15:43   ` [og12] " Thomas Schwinge
2023-04-28  8:48   ` Tobias Burnus
2023-04-28  9:31     ` Thomas Schwinge
2023-04-28 10:51       ` Tobias Burnus
2023-04-04 14:40 ` [Patch] libgomp/nvptx: Prepare for reverse-offload callback handling Thomas Schwinge
2023-04-28  8:28   ` Tobias Burnus
2023-04-28  9:23     ` Thomas Schwinge

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