[Nouveau] [PATCH] drm/nouveau: fix __nouveau_fence_wait performance regression

[Marcin Slusarz]

On Sun, Feb 13, 2011 at 09:38:04PM +0100, Marcin Slusarz wrote:
> Combination of locking and interchannel synchronization changes
> uncovered poor behaviour of nouveau_fence_wait, which on HZ=100
> configuration could waste up to 10 ms per call.
> Depending on application, it lead to 10-30% FPS regression.
> To fix it, shorten thread sleep time to 0.1 ms and ensure
> spinning happens for at least one *full* tick.
> 
> Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_fence.c |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index 221b846..75ba5e2 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -27,6 +27,9 @@
>  #include "drmP.h"
>  #include "drm.h"
>  
> +#include <linux/ktime.h>
> +#include <linux/hrtimer.h>
> +
>  #include "nouveau_drv.h"
>  #include "nouveau_ramht.h"
>  #include "nouveau_dma.h"
> @@ -230,9 +233,12 @@ int
>  __nouveau_fence_wait(void *sync_obj, void *sync_arg, bool lazy, bool intr)
>  {
>  	unsigned long timeout = jiffies + (3 * DRM_HZ);
> -	unsigned long sleep_time = jiffies + 1;
> +	unsigned long sleep_time = jiffies + 2;
> +	ktime_t t;
>  	int ret = 0;
>  
> +	t = ktime_set(0, NSEC_PER_MSEC / 10);
> +
>  	while (1) {
>  		if (__nouveau_fence_signalled(sync_obj, sync_arg))
>  			break;
> @@ -245,7 +251,7 @@ __nouveau_fence_wait(void *sync_obj, void *sync_arg, bool lazy, bool intr)
>  		__set_current_state(intr ? TASK_INTERRUPTIBLE
>  			: TASK_UNINTERRUPTIBLE);
>  		if (lazy && time_after_eq(jiffies, sleep_time))
> -			schedule_timeout(1);
> +			schedule_hrtimeout(&t, HRTIMER_MODE_REL);
>  
>  		if (intr && signal_pending(current)) {
>  			ret = -ERESTARTSYS;
> -- 
> 1.7.4.rc3
> 

http://www.youtube.com/watch?v=arCITMfxvEc#t=2m11s

Your favourite machine ;),
Marcin