[Intel-gfx] [PATCH 03/18] drm/i915: "Race-to-idle" after switching to the kernel context

[Chris Wilson]

Quoting Mika Kuoppala (2018-05-25 13:22:55)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > During suspend we want to flush out all active contexts and their
> > rendering. To do so we queue a request from the kernel's context, once
> > we know that request is done, we know the GPU is completely idle. To
> > speed up that switch bump the GPU clocks.
> >
> > Switching to the kernel context prior to idling is also used to enforce
> > a barrier before changing OA properties, and when evicting active
> > rendering from the global GTT. All cases where we do want to
> > race-to-idle.
> >
> > v2: Limit the boosting to only the switch before suspend.
> > v3: Limit it to the wait-for-idle on suspend.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: David Weinehall <david.weinehall at linux.intel.com>
> > Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> > Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com> #v1
> > Tested-by: David Weinehall <david.weinehall at linux.intel.com> #v1
> > ---
> >  drivers/gpu/drm/i915/i915_gem.c     | 27 +++++++++++++++++++++++++--
> >  drivers/gpu/drm/i915/i915_request.h |  1 +
> >  2 files changed, 26 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index c93f5dcb1d82..7b5544efa0ba 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -3704,7 +3704,29 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
> >  
> >  static int wait_for_timeline(struct i915_timeline *tl, unsigned int flags)
> >  {
> > -     return i915_gem_active_wait(&tl->last_request, flags);
> > +     struct i915_request *rq;
> > +     long ret;
> > +
> > +     rq = i915_gem_active_get_unlocked(&tl->last_request);
> > +     if (!rq)
> > +             return 0;
> > +
> > +     /*
> > +      * "Race-to-idle".
> > +      *
> > +      * Switching to the kernel context is often used a synchronous
> > +      * step prior to idling, e.g. in suspend for flushing all
> > +      * current operations to memory before sleeping. These we
> > +      * want to complete as quickly as possible to avoid prolonged
> > +      * stalls, so allow the gpu to boost to maximum clocks.
> > +      */
> > +     if (flags & I915_WAIT_FOR_IDLE_BOOST)
> > +             gen6_rps_boost(rq, NULL);
> > +
> > +     ret = i915_request_wait(rq, flags, MAX_SCHEDULE_TIMEOUT);
> 
> I pondered about the boost flag falling through into wait.
> But they are flags on wait domain so no reason to split/limit.

Indeed,

> >  #define I915_WAIT_INTERRUPTIBLE      BIT(0)
> >  #define I915_WAIT_LOCKED     BIT(1) /* struct_mutex held, handle GPU reset */
> >  #define I915_WAIT_ALL                BIT(2) /* used by i915_gem_object_wait() */
> > +#define I915_WAIT_FOR_IDLE_BOOST BIT(3)

I thought was a reasonable way to share the same set of flags with
distinct regions.

Thanks for the review and discussion,
-Chris