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

[Ben Widawsky]

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 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