[Intel-gfx] [PATCH 01/12] drm: Inline drm_color_lut_extract()

[Ville Syrjälä]

On Thu, Nov 07, 2019 at 03:31:28PM +0000, Kazlauskas, Nicholas wrote:
> On 2019-11-07 10:17 a.m., Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at 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 at linux.intel.com>
> 
> Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas at 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.

Constant folding gets rid of it.

> 
> 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,
> > 
> 

-- 
Ville Syrjälä
Intel