linux-kernel - Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of per_cpu_ptr(p, raw_smp_processor

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Message-ID: <20121102181026.GY3027@linux.vnet.ibm.com>
Date:	Fri, 2 Nov 2012 11:10:26 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Shan Wei <shanwei88@...il.com>
Cc:	dipankar@...ibm.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>,
	cl@...ux-foundation.org
Subject: Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of
 per_cpu_ptr(p, raw_smp_processor_id())

On Sat, Nov 03, 2012 at 12:01:47AM +0800, Shan Wei wrote:
> From: Shan Wei <davidshan@...cent.com>
> 
> Signed-off-by: Shan Wei <davidshan@...cent.com>
> ---
>  kernel/rcutree.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 74df86b..441b945 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1960,7 +1960,7 @@ static void force_quiescent_state(struct rcu_state *rsp)
>  	struct rcu_node *rnp_old = NULL;
> 
>  	/* Funnel through hierarchy to reduce memory contention. */
> -	rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
> +	rnp = __this_cpu_read(rsp->rda->mynode);

OK, I'll bite...  Why this instead of:

	rnp = __this_cpu_read(rsp->rda)->mynode;

							Thanx, Paul

>  	for (; rnp != NULL; rnp = rnp->parent) {
>  		ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
>  		      !raw_spin_trylock(&rnp->fqslock);
> -- 
> 1.7.1
> 
> 
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