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

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Message-ID: <0000013abc646055-30441bd6-241f-436a-a356-9cd462da66ce-000000@email.amazonses.com>
Date:	Thu, 1 Nov 2012 14:33:45 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Shan Wei <shanwei88@...il.com>
cc:	jesse@...ira.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, 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.

> In addition, following usage of per_cpu_ptr can be replaced by this_cpu_read.
>
> cpu=get_cpu()
> ....
> *per_cpu_ptr(p,cpu)
> ....
> ....
> put_cpu()

Right.

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