linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

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Message-ID: <20100105180026.GG1778@basil.fritz.box>
Date:	Tue, 5 Jan 2010 19:00:26 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

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@...ux.intel.com -- Speaking for myself only.
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