From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932510AbaGWPpU (ORCPT ); Wed, 23 Jul 2014 11:45:20 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:57724 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932285AbaGWPpP (ORCPT ); Wed, 23 Jul 2014 11:45:15 -0400 MIME-Version: 1.0 In-Reply-To: <20140723153018.GY11241@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> From: Pranith Kumar Date: Wed, 23 Jul 2014 11:44:43 -0400 Message-ID: Subject: Re: [PATCH 09/16] rcu: Remove redundant check for online cpu To: Paul McKenney Cc: Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , "open list:READ-COPY UPDATE..." Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). -- Pranith