[Intel-gfx] [RFC PATCH 53/97] drm/i915/guc: Disable semaphores when using GuC scheduling

[Matthew Brost]

On Thu, May 27, 2021 at 09:41:46AM +0100, Tvrtko Ursulin wrote:
> 
> On 26/05/2021 19:15, Matthew Brost wrote:
> > On Wed, May 26, 2021 at 10:25:13AM +0100, Tvrtko Ursulin wrote:
> > > 
> > > On 25/05/2021 18:01, Matthew Brost wrote:
> > > > On Tue, May 25, 2021 at 10:52:01AM +0100, Tvrtko Ursulin wrote:
> > > > > 
> > > > > On 06/05/2021 20:14, Matthew Brost wrote:
> > > > > > Disable semaphores when using GuC scheduling as semaphores are broken in
> > > > > > the current GuC firmware.
> > > > > 
> > > > > What is "current"? Given that the patch itself is like year and a half old.
> > > > > 
> > > > 
> > > > Stale comment. Semaphore work with the firmware we just haven't enabled
> > > > them in the i915 with GuC submission as this an optimization and not
> > > > required for functionality.
> > > 
> > > How will the updated commit message look in terms of remaining reasons why
> > > semaphores won't/can't be enabled?
> > > 
> > 
> > Semaphores are an optimization and not required for basic GuC submission
> > to work properly. Disable until we have time to do the implementation to
> > enable semaphores and tune them for performance.
> > 
> > > They were a nice performance win on some media workloads although granted a
> > > lot of tweaking was required to find a good balance on when to use them and
> > > when not to.
> > > 
> > 
> > The same tweaking would have to be done for with GuC submission. Let's
> > get basic submission then tweak for performance.
> 
> I don't have fundamental complaints as longs as commit message is improved
> and it is understood the absence of semaphores is extremely likely to
> regress transcode performance tests. Latter probably doesn't matter (for
> some definition of it) unless either there will be a platform where both GuC
> and execlists can be supported, or there will be two separate platforms
> similar in hw performance in theory, both relevant to transcode customers,
> one using execlists and one using GuC.
> 

Sounds good. Already have this commit message updated in my branch and will be
included in the next post.

Matt

> Regards,
> 
> Tvrtko
> 
>