Subject: Re: DRM lock ordering fix series
From: Peter Zijlstra <peterz@infradead.org>
To: Eric Anholt <eric@anholt.net>
Cc: Andi Kleen <andi@firstfloor.org>, linux-kernel@vger.kernel.org,
       dri-devel@lists.sourceforge.net, Nick Piggin <nickpiggin@yahoo.com.au>
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Date: Sat, 28 Mar 2009 02:29:59 +0100
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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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