[Intel-gfx] [PATCH] drm/i915: Use usleep_range() in wait_for()

[Jesse Barnes]

On 03/20/2015 12:28 PM, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> msleep() can sleep for way too long, so switch wait_for() to use
> usleep_range() instead. Following a totally unscientific method
> I just picked the range as W-2W.
> 
> This cuts the i915 init time on my BSW to almost half:
> - initcall i915_init+0x0/0xa8 [i915] returned 0 after 419977 usecs
> + initcall i915_init+0x0/0xa8 [i915] returned 0 after 238419 usecs
> 
> Note that I didn't perform any other benchmarks on this so far.
> 
> Cc: Jesse Barnes <jbarnes at virtuousgeek.org>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_drv.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 6f20f3a..d2a4de0 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -56,8 +56,8 @@
>  				ret__ = -ETIMEDOUT;			\
>  			break;						\
>  		}							\
> -		if (W && drm_can_sleep())  {				\
> -			msleep(W);					\
> +		if ((W) && drm_can_sleep()) {				\
> +			usleep_range((W)*1000, (W)*2000);		\
>  		} else {						\
>  			cpu_relax();					\
>  		}							\
> 

Nice improvement!  I guess it's just because usleep_range() uses an
hrtimeout, but since we have the added slop of the range it may actually
be an improvement, power-wise too.

Reviewed-by: Jesse Barnes <jbarnes at virtuousgeek.org>