linux-kernel - Re: DRM lock ordering fix series

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Date:	Fri, 27 Mar 2009 09:36:45 -0700
From:	Eric Anholt <eric@...olt.net>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.sourceforge.net
Subject: Re: DRM lock ordering fix series

On Fri, 2009-03-27 at 09:19 -0700, Eric Anholt wrote:
> On Fri, 2009-03-27 at 10:34 +0100, Andi Kleen wrote:
> > Eric Anholt <eric@...olt.net> writes:
> > 
> > > Here's hopefully the final attempt at the lock ordering fix for GEM.  The
> > > 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 was
> > > 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).
> > 
> > 
> > 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.

Ah, I see: that's a weak stub, and there is a real implementation.  I
didn't know we could do weak stubs.

Still, needs docs badly.

-- 
Eric Anholt
eric@...olt.net                         eric.anholt@...el.com



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