From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965226AbcBQItM (ORCPT ); Wed, 17 Feb 2016 03:49:12 -0500 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:41889 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965096AbcBQItJ (ORCPT ); Wed, 17 Feb 2016 03:49:09 -0500 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Wed, 17 Feb 2016 17:48:27 +0900 From: Byungchul Park To: Ingo Molnar Cc: peterz@infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: remove an unnecessary memory access, rq->cpu in __schedule() Message-ID: <20160217084827.GD5972@X58A-UD3R> References: <1455159578-17256-1-git-send-email-byungchul.park@lge.com> <20160217083109.GB1197@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160217083109.GB1197@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 17, 2016 at 09:31:09AM +0100, Ingo Molnar wrote: > > * Byungchul Park wrote: > > > Is there any reason keeping this statement on the code? > > > > -----8<----- > > From d8a387efb8199b69b6464970d6f9fc57cbcf0ab0 Mon Sep 17 00:00:00 2001 > > From: Byungchul Park > > Date: Thu, 11 Feb 2016 11:50:53 +0900 > > Subject: [PATCH] sched: remove an unnecessary memory access, rq->cpu in > > __schedule() > > > > Remove an unnecessary assignment of variable not used any more. > > > > Signed-off-by: Byungchul Park > > --- > > kernel/sched/core.c | 1 - > > 1 file changed, 1 deletion(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 1315cec..501f5d9 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -3193,7 +3193,6 @@ static void __sched notrace __schedule(bool preempt) > > > > trace_sched_switch(preempt, prev, next); > > rq = context_switch(rq, prev, next); /* unlocks the rq */ > > - cpu = cpu_of(rq); > > } else { > > lockdep_unpin_lock(&rq->lock); > > raw_spin_unlock_irq(&rq->lock); > > There's no memory access that I can see - GCC will optimize it out. Yes, gcc will do it. So I expect no performance effect. > > Having said that, it is a dead statement so can be removed. I fixed the title > accordingly. Thank you. > > Thanks, > > Ingo