From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756053Ab2JEB1g (ORCPT ); Thu, 4 Oct 2012 21:27:36 -0400 Received: from mail.lemote.com ([222.92.8.141]:35090 "EHLO lemote.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755671Ab2JEB1e (ORCPT ); Thu, 4 Oct 2012 21:27:34 -0400 X-Greylist: delayed 543 seconds by postgrey-1.27 at vger.kernel.org; Thu, 04 Oct 2012 21:27:34 EDT Message-ID: <2316.117.81.123.89.1349397314.squirrel@mail.lemote.com> Date: Fri, 5 Oct 2012 08:35:14 +0800 (CST) Subject: Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch From: =?gb2312?Q?=B3=C2=BB=AA=B2=C5?= To: "Greg Kroah-Hartman" Cc: "Peter Zijlstra" , "Charles Wang" , "Ingo Molnar" , stable@vger.kernel.org, linux-kernel@vger.kernel.org User-Agent: SquirrelMail/1.4.11 MIME-Version: 1.0 Content-Type: text/plain;charset=gb2312 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org My opinion: The original patch "sched/nohz: Rewrite and fix load-avg computation -- again" is designed for 3.5-branch and calc_load_exit_idle() is called directly in tick_nohz_idle_exit(). So, the patch can be fully applied in 3.5 and doesn't need to fix (Add the missing call), but not fully applied in 3.6 (because code splitted) and need to fix. > On Thu, Oct 04, 2012 at 08:31:59PM +0200, Peter Zijlstra wrote: >> On Thu, 2012-10-04 at 10:46 -0700, Greg Kroah-Hartman wrote: >> > On Thu, Oct 04, 2012 at 12:11:01PM +0800, Huacai Chen wrote: >> > > Hi, Greg >> > > >> > > I found that Linux-3.5.5 accept this commit "sched: Add missing call >> > > to calc_load_exit_idle()" but I think this isn't needed. Because >> > > "5167e8d5417b sched/nohz: Rewrite and fix load-avg computation -- >> > > again not fully applied" is true for 3.6 branch, but not for 3.5 >> > > branch. >> > >> > But 5167e8d5417b is in 3.5, so shouldn't this commit still be >> necessary? >> > >> > > In 3.5 branch, calc_load_exit_idle() is already called in >> > > tick_nohz_idle_exit(), it doesn't need to be called at >> > > tick_nohz_update_jiffies() again. In 3.6 branch, some code of >> > > tick_nohz_idle_exit() is splitted to tick_nohz_restart_sched_tick() >> > > and calc_load_exit_idle() is missing by accident, so commit "sched: >> > > Add missing call to calc_load_exit_idle()" is needed. >> > >> > So this really should be dropped from 3.5? Charles, Peter, Ingo, any >> > thoughts here? >> >> Bah, lots of code movement there recently.. let me try and untangle all >> that afresh.. /me checks out v3.5.5. >> >> OK, assuming ->tick_stopped means what the label says, then we only want >> to call calc_load_enter_idle() when it flips to 1 and >> calc_load_exit_idle() when it flips back to 0, such that when an actual >> tick happens its got correct state. >> >> Now the actual patch "5167e8d5417b sched/nohz: Rewrite and fix load-avg >> computation -- again not fully applied" modifies >> tick_nohz_restart_sched_tick() which doesn't appear to exist in v3.5.5 >> and the patch fobbed it into tick_nohz_update_jiffies() which is called >> from interrupt entry when nohz-idle so that the interrupt (and possible >> tailing softirq) see a valid jiffies count. >> >> However, since we don't restart the tick, we won't be sampling load muck >> and calling calc_load_exit_idle() from there is bound to confuse state. >> >> I hope.. damn this code ;-) >> >> I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c >> contains both hunks, but in that case the fixup 749c8814f0 doesn't make >> sense, not can I find anything in merge commits using: >> >> git log -S calc_load_exit_idle kernel/time/tick-sched.c >> >> /me puzzled > > I'm puzzled as well. Any ideas if I should do anything here or not? > > greg k-h > -- 江苏中科梦兰电子科技有限公司 软件部 陈华才 E-mail: chenhc@lemote.com Web: http://www.lemote.com/ Add: 江苏省常熟市虞山镇梦兰工业园