linux-kernel - Re: DRM lock ordering fix series

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Message-Id: <1238203799.4039.437.camel@laptop>
Date:	Sat, 28 Mar 2009 02:29:59 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Eric Anholt <eric@...olt.net>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sourceforge.net,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: DRM lock ordering fix series

On Sat, 2009-03-28 at 01:58 +0100, Peter Zijlstra wrote:

> > OK.  I'm not too excited here -- 10% of 2% of the CPU time doesn't get
> > me to the 10% loss that the slow path added up to.  Most of the cost is
> > in k{un,}map_atomic of the returned pages.  
> 
> Also note that doing large gup() with gup_fast() will be undesirable due
> to it disabling IRQs. So iterating say several MB worth of pages will
> hurt like crazy. Currently all gup_fast() users do a single page lookup.

Also, what's this weird facination with 32bit, can you even buy a 32bit
only cpu these days?

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