Re: [PATCH] drm/i915: Don't continually defer the hangcheck

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@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@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@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().

-Mika

> +	timer->expires = round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
> +	add_timer(timer);
>  }
>  
>  static void ibx_irq_reset(struct drm_device *dev)
> -- 
> 2.1.3
>
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