linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: clear fencing tracking state when retiring request

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Date:	Thu, 12 Apr 2012 09:01:15 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
	Jiri Slaby <jslaby@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [Intel-gfx] [PATCH] drm/i915: clear fencing tracking state when
 retiring request

On Thu, Apr 12, 2012 at 12:38:09AM +0100, Chris Wilson wrote:
> On Thu, 12 Apr 2012 01:27:57 +0200, Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> > This fixes a regression introduce in
> s/introduce/introduced/
>  
> > commit 7dd4906586274f3945f2aeaaa5a33b451c3b4bba
> > Author: Chris Wilson <chris@...is-wilson.co.uk>
> > Date:   Wed Mar 21 10:48:18 2012 +0000
> > 
> >     drm/i915: Mark untiled BLT commands as fenced on gen2/3
> > 
> > which fixed fencing tracking for untiled blt commands.
> > 
> > A side effect of that patch was that now also untiled objects have a
> > non-zero obj->last_fenced_seqno to track when a fence can be set up
> > after a pipelined tiling change. Unfortunately this was only cleared
> > by the fence setup and teardown code, resulting in tons of untiled but
> > inactive objects with non-zero last_fenced_seqno.
> > 
> > Now after resume we completely reset the seqno tracking, both on the
> > driver side (by setting dev_priv->next_seqno = 1) and on the hw side
> > (by allocating a new hws page, which contains the seqnos). Hilarity
> > and indefinite waits ensued from the stale seqnos in
> > obj->last_fenced_seqno from before the suspend.
> > 
> > The fix is to properly clear the fencing tracking state like we
> > already do for the normal gpu rendering while moving objects off the
> > active list.
> > 
> > Reported-and-tested-by: "Rafael J. Wysocki" <rjw@...k.pl>
> > Cc: Jiri Slaby <jslaby@...e.cz>
> > Signed-Off-by: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> I spent sometime discussing whether or not we could hit a similar bug
> with a well placed change of tiling after resume, and the outcome is
> that as the fences are reset during freeze then all tiled objects that
> had been used for rendering would have been flushed (and their
> last_fenced_seqno set to 0).
> 
> So this is a new regression caused by the aforementioned patch and this
> is the cleanest fix,
> Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
Picked up for -fixes, thanks for the review.
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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