Subject: Re: DRM lock ordering fix series
From: Eric Anholt <eric@anholt.net>
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org, dri-devel@lists.sourceforge.net
In-Reply-To: <87ocvnmhqx.fsf@basil.nowhere.org>
References: <1238017510-26784-1-git-send-email-eric@anholt.net>
	 <87ocvnmhqx.fsf@basil.nowhere.org>
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Date: Fri, 27 Mar 2009 09:19:27 -0700
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On Fri, 2009-03-27 at 10:34 +0100, Andi Kleen wrote:
> Eric Anholt <eric@anholt.net> writes:
>=20
> > Here's hopefully the final attempt at the lock ordering fix for GEM.  T=
he
> > problem was introduced in .29 with the GTT mapping support.  We hashed =
out
> > a few potential fixes on the mailing list and at OSTS.  Peter's plan wa=
s
> > to use get_user_pages, but it has significant CPU overhead (10% cost to=
 text
> > rendering, though part of that is due to some dumb userland code.  But =
it's
> > dumb userland code we're all running).
>=20
>=20
> You are aware that there is a fast path now (get_user_pages_fast) which
> is significantly faster? (but has some limitations)

In the code I have, get_user_pages_fast is just a wrapper that calls the
get_user_pages in the way that I'm calling it from the DRM.

I'm assuming that that's changing.  Can you explain what the "some
limitations" is?  (Though, of course, in a comment in mm/util.c would be
better than email).

--=20
Eric Anholt
eric@anholt.net                         eric.anholt@intel.com


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