[Intel-gfx] [PATCH 1/1] Let userspace know if they can trust timeslicing by including it as part of the I915_PARAM_HAS_SCHEDULER::I915_SCHEDULER_CAP_TIMESLICING

[Daniel Vetter]

On Wed, May 26, 2021 at 11:20:13AM +0100, Tvrtko Ursulin wrote:
> 
> On 25/05/2021 15:47, Daniel Vetter wrote:
> > On Tue, May 25, 2021 at 03:19:47PM +0100, Tvrtko Ursulin wrote:
> > > 
> > > + dri-devel as per process
> > > 
> > > On 25/05/2021 14:55, Tejas Upadhyay wrote:
> > > > v2: Only declare timeslicing if we can safely preempt userspace.
> > > 
> > > Commit message got butchered up somehow so you'll need to fix that at some
> > > point.
> > > 
> > > Regards,
> > > 
> > > Tvrtko
> > > 
> > > > Fixes: 8ee36e048c98 ("drm/i915/execlists: Minimalistic timeslicing")
> > > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > > ---
> > > >    drivers/gpu/drm/i915/gt/intel_engine_user.c | 1 +
> > > >    include/uapi/drm/i915_drm.h                 | 1 +
> > > >    2 files changed, 2 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> > > > index 3cca7ea2d6ea..12d165566ed2 100644
> > > > --- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
> > > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> > > > @@ -98,6 +98,7 @@ static void set_scheduler_caps(struct drm_i915_private *i915)
> > > >    		MAP(HAS_PREEMPTION, PREEMPTION),
> > > >    		MAP(HAS_SEMAPHORES, SEMAPHORES),
> > > >    		MAP(SUPPORTS_STATS, ENGINE_BUSY_STATS),
> > > > +		MAP(TIMESLICE_BIT, TIMESLICING),
> > > >    #undef MAP
> > > >    	};
> > > >    	struct intel_engine_cs *engine;
> > > > diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> > > > index c2c7759b7d2e..af2212d6113c 100644
> > > > --- a/include/uapi/drm/i915_drm.h
> > > > +++ b/include/uapi/drm/i915_drm.h
> > > > @@ -572,6 +572,7 @@ typedef struct drm_i915_irq_wait {
> > > >    #define   I915_SCHEDULER_CAP_PREEMPTION	(1ul << 2)
> > > >    #define   I915_SCHEDULER_CAP_SEMAPHORES	(1ul << 3)
> > > >    #define   I915_SCHEDULER_CAP_ENGINE_BUSY_STATS	(1ul << 4)
> > > > +#define   I915_SCHEDULER_CAP_TIMESLICING	(1ul << 5)
> > 
> > Since this is uapi I think we should at least have some nice kerneldoc
> > that explains what exactly this is, what for (link to userspace) and all
> > that. Ideally also minimally filing in the gaps in our uapi docs for stuff
> > this references.
> 
> IIUC there is no userspace apart from IGT needing it not to fail scheduling
> tests on ADL.
> 
> Current tests use "has preemption + has semaphores" as a proxy to answer the
> "does the kernel support timeslicing" question. This stops working with the
> Guc backend because GuC decided not to support semaphores (for reasons yet
> unknown, see other thread), so explicit "has timeslicing" flag is needed in
> order for tests to know that GuC is supposed to support timeslicing, even if
> it doesn't use semaphores for inter-ring synchronisation.

Since this if for igt only: Cant we do just extend the check in igt with
an || GEN >= 12? I really hope that our future hw will continue to support
timeslicing ...

Also if it's not there yet, a shared helper to check for that (like we're
adding for relocations and stuff like that right now).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch