Quoting Tvrtko Ursulin (2020-04-07 11:50:31)
>
> On 03/04/2020 10:13, Chris Wilson wrote:
> > Let userspace know if they can trust timeslicing by including it as part
> > of the I915_PARAM_HAS_SCHEDULER::I915_SCHEDULER_CAP_TIMESLICING
> >
> > v2: Only declare timeslicing if we can safely preempt userspace.
> >
> > Fixes: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing")
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_engine.h | 3 ++-
> > drivers/gpu/drm/i915/gt/intel_engine_user.c | 5 +++++
> > include/uapi/drm/i915_drm.h | 1 +
> > 3 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> > index b469de0dd9b6..424672ee7874 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> > @@ -339,7 +339,8 @@ intel_engine_has_timeslices(const struct intel_engine_cs *engine)
> > if (!IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
> > return false;
> >
> > - return intel_engine_has_semaphores(engine);
> > + return (intel_engine_has_semaphores(engine) &&
> > + intel_engine_has_preemption(engine));
>
> This is turning off timeslicing on Gen8? Well it wouldn't have worked
> anyway, outside the batch boundaries.. so it does sound technically correct.
...
> Split uapi from Gen8 fix?
I don't regard gen8 as broken per se, for the kernel could preempt
between batches -- but under the spotlight of "can userspace use this",
it clearly cannot. Hence why I put them both together, it is not until
userspace needs to control itself, that it becomes a problem.
The igt that test this purposefully do not run on gen8 because I was
aware of the limitations. That should have been a big clue, but it
wasn't until I looked at it from an actual user's perspective did I
realise how important that little detail was. :(
-Chris
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