Re: [PATCH 0/9] drm: Limit DRM_IOCTL_WAIT_VBLANK to vblank interrupts

[Michel Dänzer <michel.daenzer@mailbox.org>]

On 5/15/26 13:55, Thomas Zimmermann wrote:
> DRM's WAIT_VBLANK ioctl synchronizes user-space clients to display
> refresh. This is meaningless with vblank timers, which run unrelated
> to the hardware's vblank.
> 
> Disable the ioctl for simulated vblanks. Set DRM_VBLANK_FLAG_SIMULATED
> for CRTCs with simulated vblank events in all such drivers. The vblank
> timers of these devices still rate-limit the number of page-flip events
> to match the display refresh.
> 
> According to maintainers, user-space compositors do not require the ioctl
> for rate-limitting display output. Weston and Kwin rely on page-flip
> events. Mutter uses and internal timer to limit the number of display
> updates per second.

Actually mutter fundamentally relies on atomic commit completion events for that, same as Weston & KWin. Mutter uses the WAIT_VBLANK ioctl only for minimizing input → output latency (which can hide issues when completion of atomic commits isn't properly throttled).


(Just a side not on the cover letter, no objections to the patches themselves)


-- 
Earthling Michel Dänzer       \        GNOME / Xwayland / Mesa developer
https://redhat.com             \               Libre software enthusiast