Re: drm_sched run_job and scheduling latency

Hillf Danton
2026-03-09T18:55:58Z

On Wed, Mar 04, 2026 at 02:51:39PM -0800, Chia-I Wu wrote:
> Hi,
>
> Our system compositor (surfaceflinger on android) submits gpu jobs
> from a SCHED_FIFO thread to an RT gpu queue. However, because
> workqueue threads are SCHED_NORMAL, the scheduling latency from submit
> to run_job can sometimes cause frame misses. We are seeing this on
> panthor and xe, but the issue should be common to all drm_sched users.
>
> Using a WQ_HIGHPRI workqueue helps, but it is still not RT (and won't
> meet future android requirements). It seems either workqueue needs to
> gain RT support, or drm_sched needs to support kthread_worker.
>
As RT means (in general) to some extent that the game of eevdf is played in
__userspace__, but you are not PeterZ, so any issue like frame miss is
understandably expected.
Who made the workqueue worker a victim if the CPU cycles are not tight?
Who is the new victim of a RT kthread worker?
As RT is not free, what did you pay for it, given fewer RT success on market?