From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756376AbaGWNud (ORCPT ); Wed, 23 Jul 2014 09:50:33 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:40426 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752480AbaGWNu3 (ORCPT ); Wed, 23 Jul 2014 09:50:29 -0400 Date: Wed, 23 Jul 2014 06:50:24 -0700 From: "Paul E. McKenney" To: Pranith Kumar Cc: Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , "open list:READ-COPY UPDATE..." Subject: Re: [PATCH 09/16] rcu: Remove redundant check for online cpu Message-ID: <20140723135024.GR11241@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1406092194-13004-1-git-send-email-bobby.prani@gmail.com> <1406092194-13004-10-git-send-email-bobby.prani@gmail.com> <20140723122112.GJ11241@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14072313-7164-0000-0000-00000354089E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 23, 2014 at 08:59:06AM -0400, Pranith Kumar wrote: > On Wed, Jul 23, 2014 at 8:21 AM, Paul E. McKenney > wrote: > > On Wed, Jul 23, 2014 at 01:09:46AM -0400, Pranith Kumar wrote: > >> There are two checks for an online CPU if two if() conditions. This commit > >> simplies this by replacing it with only one check for the online CPU. > >> > >> Signed-off-by: Pranith Kumar > > > > I admit that it is very early in the morning my time, but I don't see > > this change as preserving the semantics in all cases. Please recheck > > your changes to the second check. > > > > Thanx, Paul > > I guess you must be thrown off by the complementary checks, the first > check is for cpu_online() and second is for cpu_is_offline(). :) > > Previously, if a cpu is offline, the first condition is false and the > second condition is true, so we return from the second if() condition. > The same semantics are being preserved. Fair enough! Nevertheless, I am not seeing this as a simplification. Thanx, Paul > -- > Pranith. > > > > > > >> --- > >> kernel/rcu/tree.c | 9 ++++++--- > >> 1 file changed, 6 insertions(+), 3 deletions(-) > >> > >> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > >> index 5dcbf36..8d598a2 100644 > >> --- a/kernel/rcu/tree.c > >> +++ b/kernel/rcu/tree.c > >> @@ -2602,15 +2602,18 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, > >> { > >> bool needwake; > >> > >> + if (!cpu_online(smp_processor_id())) > >> + return; > >> + > >> /* > >> * If called from an extended quiescent state, invoke the RCU > >> * core in order to force a re-evaluation of RCU's idleness. > >> */ > >> - if (!rcu_is_watching() && cpu_online(smp_processor_id())) > >> + if (!rcu_is_watching()) > >> invoke_rcu_core(); > >> > >> - /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ > >> - if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) > >> + /* If interrupts were disabled, don't invoke RCU core. */ > >> + if (irqs_disabled_flags(flags)) > >> return; > >> > >> /* > >> -- > >> 2.0.0.rc2 > >> > > > > > > -- > Pranith >