Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756404Ab2KBUTJ (ORCPT ); Fri, 2 Nov 2012 16:19:09 -0400 Received: from a193-30.smtp-out.amazonses.com ([199.255.193.30]:30564 "EHLO a193-30.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753544Ab2KBUTH (ORCPT ); Fri, 2 Nov 2012 16:19:07 -0400 Date: Fri, 2 Nov 2012 20:19:04 +0000 From: Christoph Lameter X-X-Sender: cl@gentwo.org To: "Paul E. McKenney" cc: Shan Wei , dipankar@in.ibm.com, Kernel-Maillist Subject: Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of per_cpu_ptr(p, raw_smp_processor_id()) In-Reply-To: <20121102181026.GY3027@linux.vnet.ibm.com> Message-ID: <0000013ac2c6e1f0-c10ec42d-70bb-4e24-99d6-8e70653eca83-000000@email.amazonses.com> References: <5093EE6B.3070906@gmail.com> <20121102181026.GY3027@linux.vnet.ibm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SES-Outgoing: 199.255.193.30 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1361 Lines: 36 On Fri, 2 Nov 2012, Paul E. McKenney wrote: > On Sat, Nov 03, 2012 at 12:01:47AM +0800, Shan Wei wrote: > > From: Shan Wei > > > > Signed-off-by: Shan Wei > > --- > > 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; Because this_cpu_read fetches a data word from an address. The addres is relocated using a segment prefix (which contains the offset of the current per cpu area). And the address needed here is the address of the field of mynode within a structure that has a per cpu address. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/