[PATCH mesa v4] wayland: Add support for eglSwapInterval

[Tomeu Vizoso]

>> > On 28 October 2013 11:19, Tomeu Vizoso <tomeu at tomeuvizoso.net> wrote:
>> >> I'm still concerned about platforms with high resolution displays but
>> >> relatively little memory.
>> >>
>> >> I'm thinking of the RPi, but my understanding is that Android goes to
>> >> great lengths to reduce the number of buffers that clients have to
>> >> keep, because of general memory consumption, but also because scanout
>> >> buffers are precious when you try to get the smoothest of the
>> >> experiences that is possible on these phones.
>> >>
>> >> I think we should still consider adding a flag through which the
>> >> client can tell the compositor to send the release events immediately
>> >> instead of queuing them.
>> >>
>> >> Otherwise, the compositor is making a very broad assumption on the
>> >> client's inner workings if it assumes that release events can be
>> >> queued without a negative impact on performance.
>
> I fail to see how this is such a broad assumption.  If we don't want to make
> assumptions, we should just post the event every time.  Admittedly, I don't
> know what the inside of your RPi EGL implementation looks like.  However, it
> costs almost nothing to call wl_display.sync after every attach/commit and
> it *guarantees* that you get the events.  You don't have to continuously
> sync, just sync after every attach/commit.  While it may be somewhat
> non-obvious, I don't see how calling sync once per frame is any worse than
> setting some flag somewhere.

What I fail to see is why a single sync should be enough, as we don't
know when the GPU will signal that it's done with the buffer that we
are waiting to be released.

Regards,

Tomeu

> Unless, of course, you are wanting the event absolutely as soon as it
> happens.  I'd like to see an actual use-case where doing so would save you a
> buffer.
>
> Thanks,
> --Jason Ekstrand
>