linux-kernel - Re: [PATCH 7/9] rcu: use this_cpu_ptr per-cpu helper instead of per_cpu_ptr(p, raw_smp_processor

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Message-ID: <20121031200842.GC3027@linux.vnet.ibm.com>
Date:	Wed, 31 Oct 2012 13:08:42 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Shan Wei <shanwei88@...il.com>, dipankar@...ibm.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/9] rcu:  use this_cpu_ptr per-cpu helper instead of
 per_cpu_ptr(p, raw_smp_processor_id())

On Wed, Oct 31, 2012 at 05:47:04PM +0000, Christoph Lameter wrote:
> On Wed, 31 Oct 2012, Shan Wei wrote:
> 
> > 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..3a21fcf 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_ptr(rsp->rda)->mynode;
> 
> Do
> 
> 	rnp = this_cpu_read(rsp->rda->mynode);
> 
> instad.

One thing to keep in mind -- the only purpose of this is to diffuse
memory contention.  So there is no need to disable preemption.

							Thanx, Paul

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