[Intel-gfx] [PATCH] drm/i915/gt: Treat idling as a RPS downclock event

[Lyude Paul]

Hey - almost forgot to reply to this, I actually probably won't be able to
test this properly for a while since my razer laptop is actually stuck in the
office I work at, and I legally can't get to it with COVID-19 shelter-in-
place. Sorry about that!

On Sun, 2020-03-22 at 15:40 +0000, Chris Wilson wrote:
> If we park/unpark faster than we can respond to RPS events, we never
> will process a downlock event after expiring a waitboost, and thus we
> will forever restart the GPU at max clocks even if the workload switches
> and doesn't justify full power.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/issues/1500
> Fixes: 3e7abf814193 ("drm/i915: Extract GT render power state management")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Andi Shyti <andi.shyti at intel.com>
> Cc: Lyude Paul <lyude at redhat.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_rps.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_rps.c
> b/drivers/gpu/drm/i915/gt/intel_rps.c
> index 7bf631ca560b..50884aeac49c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_rps.c
> +++ b/drivers/gpu/drm/i915/gt/intel_rps.c
> @@ -771,6 +771,19 @@ void intel_rps_park(struct intel_rps *rps)
>  	intel_uncore_forcewake_get(rps_to_uncore(rps), FORCEWAKE_MEDIA);
>  	rps_set(rps, rps->idle_freq, false);
>  	intel_uncore_forcewake_put(rps_to_uncore(rps), FORCEWAKE_MEDIA);
> +
> +	/*
> +	 * Since we will try and restart from the previously requested
> +	 * frequency on unparking, treat this idle point as a downlock
> +	 * interrupt and reduce the frequency for resume. If we park/unpark
> +	 * more frequently than the rps worker can run, we will not respond
> +	 * to any EI and never see a change in frequency.
> +	 *
> +	 * (Note the we accommodate Cherryview's limitation of only using
> +	 * an even bin by applying it to all.)
> +	 */
> +	rps->cur_freq =
> +		max_t(u8, round_down(rps->cur_freq - 1, 2), rps->min_freq);
>  }
>  
>  void intel_rps_boost(struct i915_request *rq)
-- 
Cheers,
	Lyude Paul (she/her)
	Associate Software Engineer at Red Hat