From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops
Date: Mon, 12 Sep 2011 16:23:53 +0200 [thread overview]
Message-ID: <1315837433.26517.45.camel@twins> (raw)
In-Reply-To: <20110912142305.GN7761@one.firstfloor.org>
On Mon, 2011-09-12 at 16:23 +0200, Andi Kleen wrote:
> On Mon, Sep 12, 2011 at 04:05:58PM +0200, Peter Zijlstra wrote:
> > Subject: llist: Remove cpu_relax() usage in cmpxchg loops
> > From: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Date: Mon Sep 12 15:50:49 CEST 2011
> >
> > Initial benchmarks show they're a net loss (2 socket wsm):
> >
>
> May still save power. however:
>
> > entry = cmpxchg(&head->first, old_entry, new);
> > if (entry == old_entry)
> > break;
> > - cpu_relax();
>
> You need at least a barrier() then, otherwise the compiler could
> change the memory order in the loop.
the cmpxchg is a full memory barrier and compiler barrier.
next prev parent reply other threads:[~2011-09-12 14:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-08 6:00 [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Huang Ying
2011-09-08 6:00 ` [PATCH -mm -v2 1/5] llist, Make all llist functions inline Huang Ying
2011-09-08 6:00 ` [PATCH -mm -v2 2/5] llist, Define macro to check NMI safe cmpxchg Huang Ying
2011-09-08 6:00 ` [PATCH -mm -v2 3/5] llist, Move cpu_relax after cmpxchg Huang Ying
2011-09-08 6:00 ` [PATCH -mm -v2 4/5] llist, Return whether list is empty before adding in llist_add Huang Ying
2011-09-08 6:00 ` [PATCH -mm -v2 5/5] irq_work, Use llist in irq_work Huang Ying
2011-09-12 14:05 ` [PATCH 6/5] llist: Add llist_next() Peter Zijlstra
2011-09-12 14:05 ` [PATCH 7/5] sched: Convert to use llist Peter Zijlstra
2011-09-12 14:05 ` [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops Peter Zijlstra
2011-09-12 14:23 ` Andi Kleen
2011-09-12 14:23 ` Peter Zijlstra [this message]
2011-09-12 14:47 ` Mathieu Desnoyers
2011-09-12 15:09 ` Peter Zijlstra
2011-09-12 15:24 ` Peter Zijlstra
2011-09-12 16:38 ` Andi Kleen
2011-09-12 18:53 ` Peter Zijlstra
2011-09-12 14:26 ` Avi Kivity
2011-09-12 14:32 ` Peter Zijlstra
2011-09-13 11:43 ` Avi Kivity
2011-09-13 14:22 ` Peter Zijlstra
2011-09-13 14:51 ` Avi Kivity
2011-09-13 14:53 ` Peter Zijlstra
2011-09-12 14:06 ` [PATCH -mm -v2 0/5] irq_work, Use llist in irq_work Peter Zijlstra
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