Date: Tue, 5 Jan 2010 19:00:26 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Minchan Kim <minchan.kim@gmail.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Peter Zijlstra <peterz@infradead.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "hugh.dickins" <hugh.dickins@tiscali.co.uk>,
       Nick Piggin <nickpiggin@yahoo.com.au>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
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On Tue, Jan 05, 2010 at 11:47:49AM -0600, Christoph Lameter wrote:
> On Tue, 5 Jan 2010, Andi Kleen wrote:
> 
> > > Oh well. Somebody who is bored might look at trying to make the wrapper
> > > code in arch/x86/lib/semaphore_32.S work on x86-64 too. It should make the
> > > successful rwsem cases much faster.
> >
> > Maybe, maybe not.
> 
> What we saw in the past was that the cost of acquiring exclusive
> access to the contended cachelines containing mmap_sem and rss counters
> was most important.

That cost should be about the same between the spinlock and the atomic version.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.
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