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

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Message-ID: <20101206143256.GE3158@balbir.in.ibm.com>
Date:	Mon, 6 Dec 2010 20:02:56 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.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

* Christoph Lameter <cl@...ux.com> [2010-12-01 12:13:44]:

> 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).
>

But that breaks current behaviour, we should probably initialize all
of the array to -1? 

-- 
	Three Cheers,
	Balbir
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