[Intel-gfx] [PATCH v3 05/16] drm/i915: track ring progression using seqnos

[Ben Widawsky]

On Sat, Apr 20, 2013 at 11:43:51AM -0700, Ben Widawsky wrote:
> On Thu, Apr 04, 2013 at 06:32:37PM +0300, Mika Kuoppala wrote:
> > Instead of relying in acthd, track ring seqno progression
> > to detect if ring has hung.
> > 
> > v2: put hangcheck stuff inside struct (Chris Wilson)
> > 
> > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> 
> This patch really scares me. I think we don't want to ever stop using
> ACTHD. AFAICT, ACTHD is aways something we want to track in regards to
> the GPU not making progress. (unless we're worried about cycles in the
> CS, but there, seqno would equally not help us track progress).
> 
> The two danger cases are:
> an infinite loop in a shader
> never called MI_BATCH_BUFFER_END
> 
> And for both, *I think* ACTHD won't change.

I'm wrong. I was confusing HEAD with ACTHD. ACTHD is supposed to show
the address of either the batch, or the ring. HEAD is something we could
use instead though. Just a thought.

> 
> I believe what the patch really wants is to stop using instdone, but
> continue to use ACTHD as a fallback.
> 
> I think if you can keep ACTHD around, I'd be willing to r-b this.
> 
> Discussion moved to IRC.
> 
> 
> [snip]
> -- 
> Ben Widawsky, Intel Open Source Technology Center
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-- 
Ben Widawsky, Intel Open Source Technology Center