Re: [PATCH 1/3] vulkan: Define new VK_MESA_query_timestamp extension [v2]

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Tue, 10 Jul 2018 11:02:23 -0700
"Keith Packard" <keithp@keithp.com> wrote:

> Pekka Paalanen <ppaalanen@gmail.com> writes:
> 
> > On Sat, 23 Jun 2018 12:13:53 -0500
> > Jason Ekstrand <jason@jlekstrand.net> wrote:
> >  
> >> I haven't thought through this comment all that hard but would it make 
> >> sense to have three timestamps, CPU, GPU, CPU so that you have error bars 
> >> on the GPU timestamp?  At the very least, two timestamps would be better 
> >> than one so that, when we pull it into the kernel, it can provide something 
> >> more accurate than userspace trying to grab a snapshot.  
> >
> > Hi,
> >
> > three timestamps sounds like a good idea to me, but you might want to
> > reach out to media developers (e.g. gstreamer) who have experience in
> > synchronizing different clocks and what that will actually take.  
> 
> Oh, I know that's really hard, and I don't want to solve that problem
> here. I explicitly *don't* solve it though -- I simply expose the
> ability to get correlated values in the two application-visible time
> domains that the Vulkan API already exposes (surface time and GPU
> time). How to synchronize the application as those two clocks drift
> around is outside the domain of this extension.

Hi Keith,

I did not mean you would be solving that problem. I meant that it would
be good to figure out what people actually want from the API to be able
to solve the problem themselves.


Thanks,
pq

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