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:
> Â Â Â Â Â Â Â amdgpu_mn_lock(p->mn);
> Â Â Â Â Â Â Â if (p->bo_list) {
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â for (i = p->bo_list->first_userptr;
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â i < p->bo_list->num_entries; ++i) {
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â struct amdgpu_bo *bo = p->bo_list->array[i].robj;
>
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â if
> (amdgpu_ttm_tt_userptr_needs_pages(bo->tbo.ttm)) {
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â amdgpu_mn_unlock(p->mn);
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â return -ERESTARTSYS;
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â }
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â }
> Â Â Â Â Â Â Â }
If anything changed on the page tables we restart the whole IOCTL using
-ERESTARTSYS and try again.
Regards,
Christian.
> -Daniel
