From: Chris Wilson <chris@chris-wilson.co.uk>
To: Daniel Vetter <daniel@ffwll.ch>, Keith Packard <keithp@keithp.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position
Date: Wed, 08 Feb 2012 18:17:00 +0000 [thread overview]
Message-ID: <d08817$33o163@azsmga001.ch.intel.com> (raw)
In-Reply-To: <CAKMK7uFNUGf0oEf6MbygM803H=UFD8-Ci-8RHaafdmzz0a3JeA@mail.gmail.com>
On Wed, 8 Feb 2012 19:02:47 +0100, Daniel Vetter <daniel@ffwll.ch> wrote:
> The issue is that the first one introduces a pretty decent perf
> regression, iirc Chris mentions something much large than 10x slowdown
> on certain cairo traces on sna. So we can only merge the first one
> together with the second one.
As it turns out, the cairo-traces were successfully exploiting the
ringbuffer overflow to avoid work. The reason why it eventually broke is
that when I experimented with using the BLT and semaphores, I introduced
a dependency on accurate seqno processing, which was obviously broken by
the overwriting of commands in the ringbuffer. And so is consistent with
the hangs reported by Eugeni and Ben, but we have yet to see many more
examples in the wild. Otoh, I don't think this explains the
all-generation use-after-free bug.
Net result, the 0.9s firefox-paintball result was a fantasy and the perf
gains provided by the second patch are only around 20% for the same
trace. Ergo -next material only if it passes scrutiny.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
next prev parent reply other threads:[~2012-02-08 18:17 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-08 13:34 [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position Chris Wilson
2012-02-08 13:34 ` [PATCH 2/2] drm/i915: Record the tail at each request and use it to estimate the head Chris Wilson
2012-02-08 14:51 ` Daniel Vetter
2012-02-08 18:06 ` [PATCH] " Chris Wilson
2012-02-08 18:28 ` Daniel Vetter
2012-02-08 18:56 ` Eugeni Dodonov
2012-02-08 19:21 ` Chris Wilson
2012-02-08 14:54 ` [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position Daniel Vetter
2012-02-08 17:36 ` Keith Packard
2012-02-08 18:02 ` Daniel Vetter
2012-02-08 18:17 ` Chris Wilson [this message]
2012-02-08 18:24 ` Daniel Vetter
2012-02-08 19:13 ` Keith Packard
2012-02-08 20:09 ` [PATCH 1/2] drm/i915: Record the in-flight requests at the time of a hang Chris Wilson
2012-02-08 20:09 ` [PATCH 2/2] drm/i915: Record the position of the request upon error Chris Wilson
2012-02-08 22:34 ` Daniel Vetter
2012-02-10 14:51 ` Eugeni Dodonov
2012-02-08 22:33 ` [PATCH 1/2] drm/i915: Record the in-flight requests at the time of a hang Daniel Vetter
2012-02-21 19:23 ` [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position Eric Anholt
2012-02-27 16:53 ` Jesse Barnes
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