Re: [PATCH] drm/i915: Flush the RPS bottom-half when the GPU idles

Chris Wilson
2015-12-10T12:25:58Z

On Wed, Dec 09, 2015 at 09:30:42AM -0800, Jesse Barnes wrote:
> On 12/09/2015 09:10 AM, Chris Wilson wrote:
> > Make sure that the RPS bottom-half is flushed before we set the idle
> > frequency when we decide the GPU is idle. This should prevent any races
> > with the bottom-half and setting the idle frequency, and ensures that
> > the bottom-half is bounded by the GPU's rpm reference taken for when it
> > is active (i.e. between gen6_rps_busy() and gen6_rps_idle()).
> >
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Imre Deak <imre.deak@intel.com>
> > ---
> > drivers/gpu/drm/i915/intel_pm.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index e655321385e2..bb796d4e9a3a 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -4401,11 +4401,15 @@ void gen6_rps_busy(struct drm_i915_private *dev_priv)
> >
> > void gen6_rps_idle(struct drm_i915_private *dev_priv)
> > {
> > - struct drm_device *dev = dev_priv->dev;
> > + /* Flush our bottom-half so that it does not race with us
> > + * setting the idle frequency and so that it is bounded by
> > + * our rpm wakeref.
> > + */
> > + flush_work(&dev_priv->rps.work);
> >
> > mutex_lock(&dev_priv->rps.hw_lock);
> > if (dev_priv->rps.enabled) {
> > - if (IS_VALLEYVIEW(dev))
> > + if (IS_VALLEYVIEW(dev_priv))
> > vlv_set_rps_idle(dev_priv);
> > else
> > gen6_set_rps(dev_priv->dev, dev_priv->rps.idle_freq);
> >
>
> Hah and a consistency fix snuck in there... nice.

TIL one cannot flush work from inside a workqueue.

The good news is we can quite happily squash our usage of i915_wq and
just use the regular system_wq.
-Chris

--
Chris Wilson, Intel Open Source Technology Centre