[PATCH 1/1] drm/i915: Inherit submitter nice when scheduling requests

[Dave Airlie]

On Fri, 8 Apr 2022 at 18:25, Tvrtko Ursulin
<tvrtko.ursulin at linux.intel.com> wrote:
>
>
> On 08/04/2022 08:58, Daniel Vetter wrote:
> > On Thu, Apr 07, 2022 at 04:16:27PM +0100, Tvrtko Ursulin wrote:
> >> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>
> >> Inherit submitter nice at point of request submission to account for long
> >> running processes getting either externally or self re-niced.
> >>
> >> This accounts for the current processing landscape where computational
> >> pipelines are composed of CPU and GPU parts working in tandem.
> >>
> >> Nice value will only apply to requests which originate from user contexts
> >> and have default context priority. This is to avoid disturbing any
> >> application made choices of low and high (batch processing and latency
> >> sensitive compositing). In this case nice value adjusts the effective
> >> priority in the narrow band of -19 to +20 around
> >> I915_CONTEXT_DEFAULT_PRIORITY.
> >>
> >> This means that userspace using the context priority uapi directly has a
> >> wider range of possible adjustments (in practice that only applies to
> >> execlists platforms - with GuC there are only three priority buckets), but
> >> in all cases nice adjustment has the expected effect: positive nice
> >> lowering the scheduling priority and negative nice raising it.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >
> > I don't think adding any more fancy features to i915-scheduler makes
> > sense, at least not before we've cut over to drm/sched.
>
> Why do you think so?
>
> Drm/sched has at least low/normal/high priority and surely we will keep
> the i915 context priority ABI.
>
> Then this patch is not touching the i915 scheduler at all, neither it is
> fancy.
>
> The cover letter explains how it implements the same approach as the IO
> scheduler. And it explains the reasoning and benefits. Provides an user
> experience benefit today, which can easily be preserved.

won't this cause uAPI divergence between execlists and GuC, like if
something nices to -15 or -18 with execlists and the same with GuC it
won't get the same sort of result will it?

Dave.