linux-kernel - Re: [thisops uV3 08/18] Taskstats: Use this_cpu

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Date:	Tue, 7 Dec 2010 08:39:06 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
cc:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org
Subject: Re: [thisops uV3 08/18] Taskstats: Use this_cpu_ops

On Mon, 6 Dec 2010, Balbir Singh wrote:

> > Correct. We need to subtract one from that (which will eliminate the minus
> > -1 that the inline this_cpu_inc_return creates).
> >
>
> But that breaks current behaviour, we should probably initialize all
> of the array to -1?

Not necessary. This_cpu_inc() uses an xadd instruction which retrieves
the value and then increments the memory location. Then it adds 1. The -1
eliminates that add.
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