linux-kernel - Re: [PATCH 4/9] net: openvswitch: use this_cpu

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Message-ID: <CAEP_g=-GSpSJkeZbwDpBwo-in0FYD=LjWdCFsdo7-a=ssL41nA@mail.gmail.com>
Date:	Thu, 1 Nov 2012 18:38:34 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Shan Wei <shanwei88@...il.com>, dev@...nvswitch.org,
	NetDev <netdev@...r.kernel.org>,
	Kernel-Maillist <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 4/9] net: openvswitch: use this_cpu_ptr per-cpu helper

On Thu, Nov 1, 2012 at 7:33 AM, Christoph Lameter <cl@...ux.com> wrote:
> On Thu, 1 Nov 2012, Shan Wei wrote:
>
>> But for different field in same per-cpu variable, how to guarantee n_missed
>> and n_hit are from same cpu?
>> this_cpu_read(dp->stats_percpu->n_missed);
>> [processor changed]
>> this_cpu_read(dp->stats_percpu->n_hit);
>
> What does current guarantee that? If it is guaranteed then you can use the
> __this_cpu_xxx ops.

Preemption is disabled in all of the places where writes are done and
all of the reads are from foreign CPUs.
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