On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark <robdclark@xxxxxxxxx> wrote: > On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > > > > On Wed, 22 Feb 2023 07:37:26 -0800 > > Rob Clark <robdclark@xxxxxxxxx> wrote: > > > > > On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: ... > > > > On another matter, if the application uses SET_DEADLINE with one > > > > timestamp, and the compositor uses SET_DEADLINE on the same thing with > > > > another timestamp, what should happen? > > > > > > The expectation is that many deadline hints can be set on a fence. > > > The fence signaller should track the soonest deadline. > > > > You need to document that as UAPI, since it is observable to userspace. > > It would be bad if drivers or subsystems would differ in behaviour. > > > > It is in the end a hint. It is about giving the driver more > information so that it can make better choices. But the driver is > even free to ignore it. So maybe "expectation" is too strong of a > word. Rather, any other behavior doesn't really make sense. But it > could end up being dictated by how the hw and/or fw works. It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that. See the topic of implementing triple-buffering in Mutter in order to put more work to the GPU in order to have the GPU ramp up clocks in order to not miss rendering deadlines. I don't think that patch set has landed in Mutter upstream, but I hear distributions in downstream are already carrying it. https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1383 https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441 Granted, GPU clocks are just one side of that story it seems, and triple-buffering may have other benefits. If SET_DEADLINE would fix that problem without triple-buffering, it is definitely userspace observable, expected and eventually required behaviour. Thanks, pq
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