Re: [PATCH 01/12] drm: Inline drm_color_lut_extract()

["Kazlauskas, Nicholas" <Nicholas.Kazlauskas@amd.com>]

On 2019-11-07 10:17 a.m., Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> This thing can get called several thousand times per LUT
> so seems like we want to inline it to:
> - avoid the function call overhead
> - allow constant folding
> 
> A quick synthetic test (w/o any hardware interaction) with
> a ridiculously large LUT size shows about 50% reduction in
> runtime on my HSW and BSW boxes. Slightly less with more
> reasonable LUT size but still easily measurable in tens
> of microseconds.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>

Seems reasonable to me. It would probably make sense to even split this 
further into two functions, one for high precision and one for low 
precision so it's purely a calculation and not hitting any branches.

Nicholas Kazlauskas

> ---
>   drivers/gpu/drm/drm_color_mgmt.c | 24 ------------------------
>   include/drm/drm_color_mgmt.h     | 23 ++++++++++++++++++++++-
>   2 files changed, 22 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> index 4ce5c6d8de99..19c5f635992a 100644
> --- a/drivers/gpu/drm/drm_color_mgmt.c
> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> @@ -108,30 +108,6 @@
>    * 	standard enum values supported by the DRM plane.
>    */
>   
> -/**
> - * drm_color_lut_extract - clamp and round LUT entries
> - * @user_input: input value
> - * @bit_precision: number of bits the hw LUT supports
> - *
> - * Extract a degamma/gamma LUT value provided by user (in the form of
> - * &drm_color_lut entries) and round it to the precision supported by the
> - * hardware.
> - */
> -uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision)
> -{
> -	uint32_t val = user_input;
> -	uint32_t max = 0xffff >> (16 - bit_precision);
> -
> -	/* Round only if we're not using full precision. */
> -	if (bit_precision < 16) {
> -		val += 1UL << (16 - bit_precision - 1);
> -		val >>= 16 - bit_precision;
> -	}
> -
> -	return clamp_val(val, 0, max);
> -}
> -EXPORT_SYMBOL(drm_color_lut_extract);
> -
>   /**
>    * drm_crtc_enable_color_mgmt - enable color management properties
>    * @crtc: DRM CRTC
> diff --git a/include/drm/drm_color_mgmt.h b/include/drm/drm_color_mgmt.h
> index d1c662d92ab7..069b21d61871 100644
> --- a/include/drm/drm_color_mgmt.h
> +++ b/include/drm/drm_color_mgmt.h
> @@ -29,7 +29,28 @@
>   struct drm_crtc;
>   struct drm_plane;
>   
> -uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
> +/**
> + * drm_color_lut_extract - clamp and round LUT entries
> + * @user_input: input value
> + * @bit_precision: number of bits the hw LUT supports
> + *
> + * Extract a degamma/gamma LUT value provided by user (in the form of
> + * &drm_color_lut entries) and round it to the precision supported by the
> + * hardware.
> + */
> +static inline u32 drm_color_lut_extract(u32 user_input, int bit_precision)
> +{
> +	u32 val = user_input;
> +	u32 max = 0xffff >> (16 - bit_precision);
> +
> +	/* Round only if we're not using full precision. */
> +	if (bit_precision < 16) {
> +		val += 1UL << (16 - bit_precision - 1);
> +		val >>= 16 - bit_precision;
> +	}
> +
> +	return clamp_val(val, 0, max);
> +}
>   
>   void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,
>   				uint degamma_lut_size,
> 

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