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Reply-To: christian.koenig@amd.com
Subject: Re: [Linaro-mm-sig] [PATCH 1/5] dma-buf: add optional
 invalidate_mappings callback v2
To: Daniel Vetter <daniel@ffwll.ch>, christian.koenig@amd.com
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
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From: =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
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Date: Wed, 21 Mar 2018 12:54:20 +0100
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Am 21.03.2018 um 09:28 schrieb Daniel Vetter:
> On Tue, Mar 20, 2018 at 06:47:57PM +0100, Christian König wrote:
>> Am 20.03.2018 um 15:08 schrieb Daniel Vetter:
>>> [SNIP]
>>> For the in-driver reservation path (CS) having a slow-path that grabs a
>>> temporary reference, drops the vram lock and then locks the reservation
>>> normally (using the acquire context used already for the entire CS) is a
>>> bit tricky, but totally feasible. Ttm doesn't do that though.
>> That is exactly what we do in amdgpu as well, it's just not very efficient
>> nor reliable to retry getting the right pages for a submission over and over
>> again.
> Out of curiosity, where's that code? I did read the ttm eviction code way
> back, and that one definitely didn't do that. Would be interesting to
> update my understanding.

That is in amdgpu_cs.c. amdgpu_cs_parser_bos() does a horrible dance 
with grabbing, releasing and regrabbing locks in a loop.

Then in amdgpu_cs_submit() we grab an lock preventing page table updates 
and check if all pages are still the one we want to have:
>         amdgpu_mn_lock(p->mn);
>         if (p->bo_list) {
>                 for (i = p->bo_list->first_userptr;
>                      i < p->bo_list->num_entries; ++i) {
>                         struct amdgpu_bo *bo = p->bo_list->array[i].robj;
>
>                         if 
> (amdgpu_ttm_tt_userptr_needs_pages(bo->tbo.ttm)) {
>                                 amdgpu_mn_unlock(p->mn);
>                                 return -ERESTARTSYS;
>                         }
>                 }
>         }

If anything changed on the page tables we restart the whole IOCTL using 
-ERESTARTSYS and try again.

Regards,
Christian.

> -Daniel