[Intel-gfx] [PATCH] drm/i915: Don't continually defer the hangcheck

[Chris Wilson]

On Fri, Nov 07, 2014 at 04:28:33PM +0200, Mika Kuoppala wrote:
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > With multiple rings, we may continue to render on the blitter whilst
> > executing an infinite shader on the render ring. As we currently, rearm
> > the timer with each execbuf, in this scenario the hangcheck will never
> > fire and we will never detect the lockup on the render ring. Instead,
> > only arm the timer once per hangcheck, so that hangcheck runs more
> > frequently.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_irq.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index 318a6a0724d0..82b4d742aba5 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -3039,11 +3039,16 @@ static void i915_hangcheck_elapsed(unsigned long data)
> >  void i915_queue_hangcheck(struct drm_device *dev)
> >  {
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > +	struct timer_list *timer = &dev_priv->gpu_error.hangcheck_timer;
> > +
> >  	if (!i915.enable_hangcheck)
> >  		return;
> >  
> > -	mod_timer(&dev_priv->gpu_error.hangcheck_timer,
> > -		  round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES));
> > +	if (timer_pending(timer))
> > +		return;
> > +
> 
> As this is called from both process and interrupt context, what
> keeps us safe from not messing up the timer bookkeepping? The lock in timer code?
> 
> I am thinking that the other thread will hit the BUG_ON in add_timer().

if (!timer_pending(timer))
	timer->expires = round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES));
mod_timer(timer, timer->expires);
?

Or we just switch to using delayed_work() with a slightly less risky
interface.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre