[Intel-gfx] [PATCH] drm/i915: Use max(render, media) for Baytrail busyness calculation

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> Currently, we sum the render and media cycles (on different engines) to
> compute a percentage - but we fail to factor in the duplication into the
> threshold calculations. This makes us very eager to upclock!
>

I wonder if this was intentional. However acting on behalf
of the more busy engine on the calculation smells more correct.

Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com>

> If we just consider the maximum busy cycles of either counter, we should
> have an accurate reflection on whether there are cycles to spare to
> handle the workload at this frequency.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 88b591e4c6ea..5084daf81776 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1098,8 +1098,8 @@ static bool vlv_c0_above(struct drm_i915_private *dev_priv,
>  	 * being blitted in X after being rendered in mesa. To account for
>  	 * this we need to combine both engines into our activity counter.
>  	 */
> -	c0 = now->render_c0 - old->render_c0;
> -	c0 += now->media_c0 - old->media_c0;
> +	c0 = max(now->render_c0 - old->render_c0,
> +		 now->media_c0 - old->media_c0);
>  	c0 *= mul * VLV_CZ_CLOCK_TO_MILLI_SEC;
>  
>  	return c0 >= time;
> -- 
> 2.11.0
>
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