linux-kernel - Re: [PATCH] atomic: add atomic_inc_not_zero

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Message-ID: <20101115143907.GN7269@basil.fritz.box>
Date:	Mon, 15 Nov 2010 15:39:07 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH] atomic: add atomic_inc_not_zero_hint()

> > atomic_read() and atomic_cmpxchg(). We tried prefetchw() and it was a
> > performance drop. It was with only 16 cpus contending on neighbour
> 
> Does prefetchw work? Andi claims that prefetchw is not working on
> x86 and I doubt that you ran tests on Itanium.

AMD supports it due to their MOESI protocol, but it's not supported
in MESIF as used by Intel QPI.  The kernel maps it on Intel to 
ordinary prefetch.

-Andi

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