[Intel-gfx] [TERRIBLE PATCH] Re: [regression?] i915 generating wakeups even when idle

[Andrew Lutomirski]

On Wed, Dec 8, 2010 at 1:17 PM, Andrew Lutomirski <luto at mit.edu> wrote:
> On Tue, Dec 7, 2010 at 5:13 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>> On Tue, 7 Dec 2010 16:31:24 -0500, Andrew Lutomirski <luto at mit.edu> wrote:
>>> On Tue, Dec 7, 2010 at 4:03 PM, Andrew Lutomirski <luto at mit.edu> wrote:
>>> > Hi all-
>>> >
>>> > Somewhere between Fedora 13 (with 2.6.35, I think) and Fedora 14 +
>>> > 2.6.36.1, i915 started generating exactly 50 interrupts per second
>>> > (suspiciously equal to my refresh rate) when X is running.  I have the
>>> > Xorg driver 2.12.0 (specifically
>>> > xorg-x11-drv-intel-2.12.0-6.fc14.1.x86_64).  When I switch to a text
>>> > console but leave X running, the interrupts stop.
>>> >
>>> > Any ideas what to look at?
>>>
>>> Quitting compiz fixes it.  Suspending compiz also fixes it.
>>
>> So it is the vblank interrupt. The vblank interrupt is get alive for a few
>> seconds after the last use. If it keeps going, then either the system is
>> as idle as you believe or we lost track of the last user and forget to
>> switch off the interrupt.
>>
>> drm.debug=0xf (echo 0xf > /sys/module/drm/parameters/debug) will have the
>> gory details of who/when triggers the vblank interrupt.
>> -Chris
>
> It's the seconds on the clock.  That causes activity once per second,
> which looks like this:
>

[...]

>
> Maybe that "several seconds" (5, according to the source) timer is way
> too long.  Is there any reason that drm_vblank_put doesn't turn off
> interrupts immediately (or, at the latest, on the very next vblank
> interrupt)?  After all, preventing deep sleep whenever there is
> display activity every five seconds seems like a waste of power.

This patch fixes it.  It's obviously not ready for prime time, but if
you're OK with the idea I can fix it up and submit it.

Signed-off-by: Andy Lutomirski <luto at mit.edu>

Diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 9d3a503..49eca3f 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -471,7 +471,7 @@ void drm_vblank_put(struct drm_device *dev, int crtc)

 	/* Last user schedules interrupt disable */
 	if (atomic_dec_and_test(&dev->vblank_refcount[crtc]))
-		mod_timer(&dev->vblank_disable_timer, jiffies + 5*DRM_HZ);
+		mod_timer(&dev->vblank_disable_timer, jiffies);
 }
 EXPORT_SYMBOL(drm_vblank_put);



>
> --Andy
>
>>
>> --
>> Chris Wilson, Intel Open Source Technology Centre
>>
>