Sub 16ms render but missing swap

[Daniel Stone]

Hi Joe,

On Wed, 18 Oct 2023 at 02:00, Joe M <brainsnacks at yahoo.com> wrote:
> A few questions:
>   1. What other avenues of investigation should I pursue for the swap delay? As in, why when I take 12 ms to render do I not see about 4ms for the swap call to return? My display is running in at 60hz.

Further to Emmanuel's point about GPU rendering being async (you can
validate by calling glFinish before eglSwapBuffers, which will wait
for everything to complete) - which hardware platform are you using
here, and which software stack as well? As in, do your Weston +
drivers + etc come from upstream projects or are they provided by a
vendor?

>   2. Has EGL been optimized to use the available wayland callbacks and maximize available client drawing time?

Yes, very much.

>   3. Does EGL leverage "weston_direct_display_v1" when available? What's required to take advantage of it in the app code? (ie. run fullscreen?)

No need. We bypass composition as much as we possibly can. You can try
using weston-simple-egl with the flag to use direct-display if you
want to satisfy yourself, but it's in no way required to bypass GPU
composition and use the display controller to scan out.

Cheers,
Daniel