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

[Imre Deak <imre.deak@intel.com>]

On ke, 2015-12-09 at 17:10 +0000, 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);

A (spurious) RPS interrupt could still reschedule the work, so could we
also explicitly disable the interrupts? Meaning to use
gen6_{disable,enable}_rps_interrupts() in gen6_rps_{idle,busy} and
making sure vlv_set_rps_idle(), gen6_set_rps() would not re-enable the
interrupts.

That would also make it possible to
remove gen6_{disable,enable}_rps_interrupts() from the 
suspend/resume path.

>  	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);
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