[Mesa-dev] [PATCH v3 0/4] Disable glthread if libX11 isn't thread-safe

[Eric Anholt]

Gregory Hainaut <gregory.hainaut at gmail.com> writes:

> On 5/8/17, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>> Having a look at Xlib might be good indeed.
>>
>> Then again, the solution you've proposed looks perfectly reasonable,
>> IMHO. It handles the problem _now_ and should also work when/if we
>> address Xlib.
>> I'll take another look today/tomorrow, but I think the series is
>> perfectly fine to land as-is.
>>
>> Thanks
>> Emil
>
> Hello Emil,
>
> Yes you're right. And potentially it can be back-ported to stable
> branch. Besides it would allow to know which applications aren't X
> thread safe. And potentially app owners can fix the issue too.
>
> By the way, I don't have commit access so feel free to push the series :)
>
> On 5/8/17, Eric Anholt <eric at anholt.net> wrote:
>> gregory hainaut <gregory.hainaut at gmail.com> writes:
>>
>>> On Fri, 5 May 2017 17:45:01 +0200
>>> Axel Davy <axel.davy at normalesup.org> wrote:
>>>
>>>> Hi,
>>>>
>>>> There should be very few X11 calls while rendering (basically only at
>>>> the beginning or end of a frame).
>>>>
>>>> Why not just always run these calls in the main thread (and wait for
>>>> glthread work to finish) ?
>>>>
>>>> That's basically what we do for gallium nine.
>>>>
>>>> Yours,
>>>>
>>>> Axel
>>>
>>> Hello Axel,
>>>
>>> Yes it is another possibility. It would requires to track gl calls that
>>> end up in X11.
>>> I'm not sure if there is an easy way to list all those gl functions. There
>>> are at least the
>>> draw calls and maybe the clear operations. Besides I'm afraid that we will
>>> need to handle
>>> various corner cases of the OpenGL API. It is doable but likely more
>>> complicated.
>>
>> General GL calls (draws, clears) won't call X11 except for DRI2's
>> GetBuffers.  If you're in DRI3, I believe you won't need to worry about
>> that at all.
>>
>> I think this patch is a good start, though.
>>
>
> Hello Eric,
>
> Indeed I saw this behavior on Nouveau. I got a crash on
> GetBuffersWithFormat on DRI2 but it was fine on DRI3. I still kept the
> check on GLX/DRI3 because I don't know if we have a strong guarantee
> that X11 is never used.

I would be surprised if there was a path that hit X through GL calls as
opposed to the window system, with DRI3.  GetBuffersWithFormat was the
problem.
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