From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030189Ab2CIP7t (ORCPT ); Fri, 9 Mar 2012 10:59:49 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:36709 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964913Ab2CIP7q (ORCPT ); Fri, 9 Mar 2012 10:59:46 -0500 Date: Thu, 8 Mar 2012 11:14:39 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, patches@linaro.org Subject: Re: [PATCH 2/6] Don't touch the snap in srcu_readers_active() Message-ID: <20120308191439.GL2348@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1331023359-6987-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-2-git-send-email-laijs@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1331027858-7648-2-git-send-email-laijs@cn.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12030915-6148-0000-0000-0000041F7ACC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 06, 2012 at 05:57:34PM +0800, Lai Jiangshan wrote: > srcu_readers_active() is called without the mutex, but it touch the snap. > also achieve better cache locality a little > > Signed-off-by: Lai Jiangshan Queued with updated commit-log message, thank you! Thanx, Paul Expand the calls to srcu_readers_active_idx() from srcu_readers_active() inline. This change improves cache locality by interating over the CPUs once rather than twice. > --- > kernel/srcu.c | 9 ++++++++- > 1 files changed, 8 insertions(+), 1 deletions(-) > > diff --git a/kernel/srcu.c b/kernel/srcu.c > index b6b9ea2..fbe2d5f 100644 > --- a/kernel/srcu.c > +++ b/kernel/srcu.c > @@ -181,7 +181,14 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx) > */ > static int srcu_readers_active(struct srcu_struct *sp) > { > - return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1); > + int cpu; > + unsigned long sum = 0; > + > + for_each_possible_cpu(cpu) { > + sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]); > + sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]); > + } > + return sum & SRCU_REF_MASK; > } > > /** > -- > 1.7.4.4 >