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

[Marcin Slusarz]

On Tue, Mar 08, 2011 at 08:24:26AM +1000, Ben Skeggs wrote:
> On Mon, 2011-03-07 at 18:18 +0000, Maarten Maathuis wrote:
> > On Fri, Mar 4, 2011 at 4:49 PM, Marcin Slusarz <marcin.slusarz at gmail.com> wrote:
> > > 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
> > >>
> > >
> > > ping again
> > > _______________________________________________
> > > Nouveau mailing list
> > > Nouveau at lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/nouveau
> > >
> > 
> > This looks ok to me, but I would like to get Ben Skeggs ok on this one
> > as well. So i've CC'ed him, hopefully he'll notice :-)
> Ah sorry, I have actually looked at this quite a while back but came to
> no solid conclusion.
> 
> While yes, I did see some minor performance improvement from it, I also
> notice that now we once again get 100% CPU usage while an app is waiting
> for the GPU a lot..

It's not "minor" performance improvement:

without this patch (FPS):
nexuiz:    53
wop:       181
tremulous: 157
wsw0.5:    89
glxgears:  730

with:
nexuiz:    63   (+18%)
wop:       248  (+37%)
tremulous: 156  (-0.6%)
wsw0.5:    91   (+2%)
glxgears:  1054 (+44%)


Ok, so you are worried about CPU usage... Let's see what will happen if
I remove spinning added by "drm/nouveau: Spin for a bit in 
nouveau_fence_wait() before yielding the CPU".

reduced version (attached):
nexuiz:    62
wop:       248
trem:      157
wsw0.5:    90
glxgears:  1055

Good enough?

---
From: Marcin Slusarz <marcin.slusarz at gmail.com>
Subject: [PATCH] drm/nouveau: fix __nouveau_fence_wait performance regression

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.

Additionally, remove spinning (added by "drm/nouveau: Spin for
a bit in nouveau_fence_wait() before yielding the CPU"), because
it's not needed anymore.

Signed-off-by: Marcin Slusarz <marcin.slusarz at gmail.com>
---
 drivers/gpu/drm/nouveau/nouveau_fence.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index a244702..010243b 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"
@@ -229,9 +232,11 @@ 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;
+	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;
@@ -243,8 +248,8 @@ __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);
+		if (lazy)
+			schedule_hrtimeout(&t, HRTIMER_MODE_REL);
 
 		if (intr && signal_pending(current)) {
 			ret = -ERESTARTSYS;
-- 
1.7.4.rc3