Re: ✗ Fi.CI.BAT: failure for series starting with [1/6] dma-buf: add dynamic DMA-buf handling v13

[Koenig, Christian]

Am 07.08.19 um 23:19 schrieb Daniel Vetter:
> On Wed, Jul 31, 2019 at 10:55:02AM +0200, Daniel Vetter wrote:
>> On Thu, Jun 27, 2019 at 09:28:11AM +0200, Christian König wrote:
>>> Hi Daniel,
>>>
>>> those fails look like something random to me and not related to my patch
>>> set. Correct?
>> First one I looked at has the reservation_obj all over:
>>
>> https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_13438/fi-cml-u/igt@gem_exec_fence@basic-busy-default.html
>>
>> So 5 second guees is ... probably real?
>>
>> Note that with the entire lmem stuff going on right now there's massive
>> discussions about how we're doing resv_obj vs obj->mm.lock the wrong way
>> round in i915, so I'm not surprised at all that you managed to trip this.
>>
>> The way I see it right now is that obj->mm.lock needs to be limited to
>> dealing with the i915 shrinker interactions only, and only for i915 native
>> objects. And for dma-bufs we need to make sure it's not anywhere in the
>> callchain. Unfortunately that's a massive refactor I guess ...
> Thought about this some more, aside from just breaking i915 or waiting
> until it's refactored (Both not awesome) I think the only option is get
> back to the original caching. And figure out whether we really need to
> take the direction into account for that, or whether upgrading to
> bidirectional unconditionally won't be ok. I think there's only really two
> cases where this matters:
>
> - display drivers using the cma/dma_alloc helpers. Everything is allocated
>    fully coherent, cpu side wc, no flushing.
>
> - Everyone else (on platforms where there's actually some flushing going
>    on) is for rendering gpus, and those always map bidirectional and want
>    the mapping cached for as long as possible.
>
> With that we could go back to creating the cached mapping at attach time
> and avoid inflicting the reservation object lock to places that would keel
> over.
>
> Thoughts?

Actually we had a not so nice internal mail thread with our hardware 
guys and it looks like we have tons of hardware bugs/exceptions that 
sometimes PCIe BARs are only readable or only writable. So it turned out 
that always caching with bidirectional won't work for us either.

Additional to that I'm not sure how i915 actually triggered the issue, 
cause with the current code that shouldn't be possible.

But independent of that I came to the conclusion that we first need to 
get to a common view of what the fences in the reservation mean or 
otherwise the whole stuff here isn't going to work smooth either.

So working on that for now and when that's finished I will come back to 
this problem here again.

Regards,
Christian.


> -Daniel
>