From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH v2 04/16] drm/i915: Resurrect ring kicking
 for semaphores, selectively
Date: Sun, 17 Mar 2013 22:53:54 +0100
Message-ID: <20130317215354.GG9021@phenom.ffwll.local>
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To: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org, miku@iki.fi, Ben Widawsky <ben@bwidawsk.net>
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On Thu, Mar 14, 2013 at 05:52:05PM +0200, Mika Kuoppala wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> Once we thought we got semaphores working, we disabled kicking the ring
> if hangcheck fired whilst waiting upon a ring as it was doing more harm
> than good:
> 
> commit 4e0e90dcb8a7df1229c69e30abebb59b0b3c2a1f
> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> Date:   Wed Dec 14 13:56:58 2011 +0100
> 
>     drm/i915: kicking rings stuck on semaphores considered harmful
> 
> However, life is never that easy and semaphores are still causing
> problems whereby the value written by one ring (bcs) is not being
> propagated to the waiter (rcs). Thus the waiter never wakes up and we
> declare the GPU hung, which often has unfortunate consequences, even if
> we successfully reset the GPU.
> 
> But the GPU is idle as it has completed the work, just didn't notify its
> clients. So we can detect the incomplete wait during hang check and
> probe the target ring to see if has indeed emitted the breadcrumb seqno
> following the work and then and only then kick the waiter.
> 
> Based on a suggestion by Ben Widawsky.
> 
> v2: cross-check wait with iphdr. fix signaller calculation.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=54226
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Ben Widawsky <ben@bwidawsk.net>
> Acked-by: Ben Widawsky <ben@bwidawsk.net>

I'll throw in the towel, let's all hail duct-tape. Queued for -next,
thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch