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

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Date:	Wed, 01 Dec 2010 19:06:26 +0100
From:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	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,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [thisops uV3 08/18] Taskstats: Use this_cpu_ops

Hello Christoph,

On Tue, 2010-11-30 at 13:07 -0600, Christoph Lameter wrote:
> plain text document attachment (this_cpu_taskstats)
> Use this_cpu_inc_return in one place and avoid ugly __raw_get_cpu in another.
> 
> Cc: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 
> ---
>  kernel/taskstats.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6/kernel/taskstats.c
> ===================================================================
> --- linux-2.6.orig/kernel/taskstats.c	2010-11-30 10:06:35.000000000 -0600
> +++ linux-2.6/kernel/taskstats.c	2010-11-30 10:10:14.000000000 -0600
> @@ -89,8 +89,7 @@ static int prepare_reply(struct genl_inf
>  		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?

Maybe that does not hurt here, Balbir?

>  		reply = genlmsg_put(skb, 0, seq, &family, 0, cmd);
>  	} else
> @@ -581,7 +580,7 @@ void taskstats_exit(struct task_struct *
>  		fill_tgid_exit(tsk);
>  	}
> 
> -	listeners = &__raw_get_cpu_var(listener_array);
> +	listeners = __this_cpu_ptr(listener_array);
>  	if (list_empty(&listeners->list))
>  		return;
> 
> 


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