From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933124AbaGWTPu (ORCPT ); Wed, 23 Jul 2014 15:15:50 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:51957 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932514AbaGWTPs (ORCPT ); Wed, 23 Jul 2014 15:15:48 -0400 Date: Wed, 23 Jul 2014 12:15:42 -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: <20140723191542.GA9398@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> <20140723135024.GR11241@linux.vnet.ibm.com> <20140723142314.GV11241@linux.vnet.ibm.com> <20140723153018.GY11241@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: 14072319-7164-0000-0000-000003562311 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 23, 2014 at 11:44:43AM -0400, Pranith Kumar wrote: > On Wed, Jul 23, 2014 at 11:30 AM, Paul E. McKenney > wrote: > > On Wed, Jul 23, 2014 at 11:11:45AM -0400, Pranith Kumar wrote: > >> On Wed, Jul 23, 2014 at 10:23 AM, Paul E. McKenney > >> wrote: > >> > On Wed, Jul 23, 2014 at 10:12:54AM -0400, Pranith Kumar wrote: > >> >> On Wed, Jul 23, 2014 at 9:50 AM, Paul E. McKenney > >> >> wrote: > >> >> > 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. > >> >> > >> >> I am not sure what you mean here, do you mean that both the checks are > >> >> actually required? > >> > > >> > I mean that the current compound tests each mean something. Pulling out > >> > the offline test adds lines of code and obscures that meaning. This means > >> > that it is easier (for me, anyway) to see why the current code is correct > >> > than it is to see why your suggested change is correct. > >> > > >> > >> That is a valid point. I did not mean to reduce readability of the > >> code. Just trying to avoid the overhead of smp_processor_id(). > >> > >> Not sure if you would prefer this, but how about the following? > > > > If you change the "awake" to something like "am_online", I could get > > behind this one. > > OK! I will submit that in the next series(with the zalloc check). You caught me at a weak moment... This change just adds an extra line of code and doesn't really help anything. So please leave this one out. Thanx, Paul