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