Re: [PATCH 4/4] drm/i915: Use czclk_freq in vlv c0 residency calculations

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

On Thu, 2015-09-24 at 23:29 +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Replace the use of mem_freq/4 with czclk_freq in the vlv c0 residency
> calculations.
> 
> Also deal with VLV_COUNT_RANGE_HIGH which affects all RCx residency
> counters. We have just enough bits to do this without intermediate
> divisions.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 07c87e0..d78ef64 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -998,12 +998,16 @@ static bool vlv_c0_above(struct drm_i915_private *dev_priv,
>  			 int threshold)
>  {
>  	u64 time, c0;
> +	unsigned int mul = 100;
>  
>  	if (old->cz_clock == 0)
>  		return false;
>  
> +	if (I915_READ(VLV_COUNTER_CONTROL) & VLV_COUNT_RANGE_HIGH)
> +		mul <<= 8;

Could've been a separate patch.

> +
>  	time = now->cz_clock - old->cz_clock;
> -	time *= threshold * dev_priv->mem_freq;
> +	time *= threshold * dev_priv->czclk_freq;

Not introduced in this patch, but the above doesn't look correct to me.
Time is cycles _divided_ by frequency, so imo the above should be either
a division, or better we should calculate c0 (10ns) cycles here.

>  
>  	/* Workload can be split between render + media, e.g. SwapBuffers
>  	 * being blitted in X after being rendered in mesa. To account for
> @@ -1011,7 +1015,7 @@ static bool vlv_c0_above(struct drm_i915_private *dev_priv,
>  	 */
>  	c0 = now->render_c0 - old->render_c0;
>  	c0 += now->media_c0 - old->media_c0;
> -	c0 *= 100 * VLV_CZ_CLOCK_TO_MILLI_SEC * 4 / 1000;
> +	c0 *= mul * VLV_CZ_CLOCK_TO_MILLI_SEC;

Based on the above this would need to be fixed too.

The above can be done as a follow-up if needed; this patch does what it
says, so:
Reviewed-by: Imre Deak <imre.deak@intel.com>

>  
>  	return c0 >= time;
>  }


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