Re: [PATCH] drm/msm: Avoid rounding down to zero jiffies

[Dmitry Baryshkov]

On 25/03/2023 00:00, Rob Clark wrote:
> From: Rob Clark <robdclark@xxxxxxxxxxxx>
>
> If userspace asked for a timeout greater than zero, but less than a
> jiffy, they clearly weren't planning on spinning.  So it is better
> to round up to one.
>
> This fixes an issue with supertuxkart that was (for some reason)
> spinning on a gl sync with 1ms timeout.  CPU time for a demo lap
> drops from:
>
>    15.83user 20.98system 0:47.46elapsed 77%CPU
>
> to:
>
>    8.84user 2.30system 0:46.67elapsed 23%CPU

Interesting. We potentially increased the timeout, but the overall 
(elapsed) time has decreased. Nevertheless:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/msm/msm_drv.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index 9f0c184b02a0..7936aa6cad03 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -548,7 +548,7 @@ static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
>   		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
>   	}
>   
> -	return clamp(remaining_jiffies, 0LL, (s64)INT_MAX);
> +	return clamp(remaining_jiffies, 1LL, (s64)INT_MAX);
>   }
>   
>   /* Driver helpers */

--
With best wishes
Dmitry