Date: Wed, 1 Dec 2010 12:13:44 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>
cc: akpm@linux-foundation.org, Pekka Enberg <penberg@cs.helsinki.fi>,
        linux-kernel@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tejun Heo <tj@kernel.org>, linux-mm@kvack.org,
        Balbir Singh <balbir@linux.vnet.ibm.com>
Subject: Re: [thisops uV3 08/18] Taskstats: Use this_cpu_ops
In-Reply-To: <1291226786.2898.22.camel@holzheu-laptop>
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References: <20101130190707.457099608@linux.com>  <20101130190845.819605614@linux.com> <1291226786.2898.22.camel@holzheu-laptop>
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On Wed, 1 Dec 2010, Michael Holzheu wrote:

> >  		return -ENOMEM;
> >
> >  	if (!info) {
> > -		int seq = get_cpu_var(taskstats_seqnum)++;
> > -		put_cpu_var(taskstats_seqnum);
> > +		int seq = this_cpu_inc_return(taskstats_seqnum);
>
> Hmmm, wouldn't seq now always be one more than before?
>
> I think that "seq = get_cpu_var(taskstats_seqnum)++" first assigns
> taskstats_seqnum to seq and then increases the value in contrast to
> this_cpu_inc_return() that returns the already increased value, correct?

Correct. We need to subtract one from that (which will eliminate the minus
-1 that the inline this_cpu_inc_return creates).

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