Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751500AbdFGAPI (ORCPT ); Tue, 6 Jun 2017 20:15:08 -0400 Received: from LGEAMRELO12.lge.com ([156.147.23.52]:60436 "EHLO lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751419AbdFGAPH (ORCPT ); Tue, 6 Jun 2017 20:15:07 -0400 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Wed, 7 Jun 2017 09:14:54 +0900 From: Byungchul Park To: Juri Lelli Cc: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@gmail.com, rostedt@goodmis.org, kernel-team@lge.com Subject: Re: [PATCH 2/2] sched/deadline: Don't return invalid cpu in cpudl_maximum_cpu() Message-ID: <20170607001454.GE3623@X58A-UD3R> References: <1496388663-29067-1-git-send-email-byungchul.park@lge.com> <1496388663-29067-2-git-send-email-byungchul.park@lge.com> <20170606151225.xlhrnh2usajmlu52@e106622-lin> <20170606234224.GD3623@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170606234224.GD3623@X58A-UD3R> 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 Content-Length: 2172 Lines: 73 On Wed, Jun 07, 2017 at 08:42:24AM +0900, Byungchul Park wrote: > On Tue, Jun 06, 2017 at 04:12:25PM +0100, Juri Lelli wrote: > > Hi, > > > > On 02/06/17 16:31, Byungchul Park wrote: > > > When the heap tree is empty, cp->elements[0].cpu has meaningless value. > > Hi, > > The meaningless value is 0. > > > > We need to consider the case. > > > > > > Signed-off-by: Byungchul Park > > > --- > > > kernel/sched/cpudeadline.c | 3 ++- > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c > > > index d4a6963..9b314a9 100644 > > > --- a/kernel/sched/cpudeadline.c > > > +++ b/kernel/sched/cpudeadline.c > > > @@ -110,7 +110,8 @@ static void cpudl_heapify(struct cpudl *cp, int idx) > > > > > > static inline int cpudl_maximum_cpu(struct cpudl *cp) > > > { > > > - return cp->elements[0].cpu; > > > + int cpu = cp->elements[0].cpu; > > > + return cp->elements[cpu].idx == IDX_INVALID ? -1 : cpu; > > > > Mmm, don't we get a WARN from cpumask_check() if we return -1 here? > > The function does not return -1 without my patch. > > Right? Or the following patch would be needed, instead. ----->8----- >From cada1345bf0ff8e6b5743999509d2abcacd79a9e Mon Sep 17 00:00:00 2001 From: Byungchul Park Date: Wed, 7 Jun 2017 09:05:34 +0900 Subject: [PATCH 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value Currently, when the heap tree is empty, cpudl_maximum_cpu() returns 0, which causes unnecessary migration. It has to return an invalid value e.g. -1 to prevent that. Signed-off-by: Byungchul Park --- kernel/sched/cpudeadline.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index d4a6963..0f67cea 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -266,8 +266,10 @@ int cpudl_init(struct cpudl *cp) return -ENOMEM; } - for_each_possible_cpu(i) + for_each_possible_cpu(i) { + cp->elements[i].cpu = -1; cp->elements[i].idx = IDX_INVALID; + } return 0; } -- 1.9.1