From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Wang Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123 native_smp_send_reschedule, round 2 Date: Mon, 20 May 2013 15:25:04 +0800 Message-ID: <5199CFD0.9030101@linux.vnet.ibm.com> References: <20130509125040.GF27333@pd.tnic> <20130509125859.GG27333@pd.tnic> <20130515184528.GO4442@linux.vnet.ibm.com> <20130515224358.GF11783@pd.tnic> <20130515235512.GT4442@linux.vnet.ibm.com> <20130517135641.GF23035@pd.tnic> <51999591.8030401@linux.vnet.ibm.com> <20130520045023.GA12690@pd.tnic> <5199C169.7060504@linux.vnet.ibm.com> <20130520064727.GD12690@pd.tnic> <5199C990.3020602@linux.vnet.ibm.com> <5199CB59.1020309@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from e28smtp09.in.ibm.com ([122.248.162.9]:33050 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751611Ab3ETHZU (ORCPT ); Mon, 20 May 2013 03:25:20 -0400 Received: from /spool/local by e28smtp09.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 20 May 2013 12:51:25 +0530 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar Cc: Borislav Petkov , Tejun Heo , "Paul E. McKenney" , Jiri Kosina , Frederic Weisbecker , Tony Luck , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , rjw@sisk.pl, cpufreq@vger.kernel.org, linux-pm@vger.kernel.org Hi, Viresh On 05/20/2013 03:12 PM, Viresh Kumar wrote: > Hi Michael, > > I haven't followed this mail chain earlier and saw this mail only as I am > added in cc now. I probably have answers to few questions here: Thanks for your quick respond :) > > On 20 May 2013 12:36, Michael Wang wrote: >> On 05/20/2013 02:58 PM, Michael Wang wrote: >>> On 05/20/2013 02:47 PM, Borislav Petkov wrote: >>>> On Mon, May 20, 2013 at 02:23:37PM +0800, Michael Wang wrote: >>>>> On 05/20/2013 12:50 PM, Borislav Petkov wrote: >>>>> So there are two questions here: >>>>> 1. Is gov_queue_work() want to queue the work on offline cpu? > > No. We are only working with online cpus now in cpufreq core and governors. > >>> Besides, the cpu gov_queue_work() is using 'policy->cpus' which seems to >>> be updated during UP DOWN notify, I think they are supposed to be online. >>> >>> But we need expert in cpufreq to confirm all these... > > I confirm this. policy->cpus only contains online cpus.. and > policy->related_cpus > always contain online+offline cpus. Nice to be confirmed :) > >> And I guess this may help to reduce the chance to trigger WARN: >> >> diff --git a/drivers/cpufreq/cpufreq_governor.c >> b/drivers/cpufreq/cpufreq_governor.c >> index 443442d..0f96013 100644 >> --- a/drivers/cpufreq/cpufreq_governor.c >> +++ b/drivers/cpufreq/cpufreq_governor.c >> @@ -180,7 +180,7 @@ void gov_queue_work(struct dbs_data *dbs_data, >> struct cpufreq_policy *policy, >> if (!all_cpus) { >> __gov_queue_work(smp_processor_id(), dbs_data, delay); >> } else { >> - for_each_cpu(i, policy->cpus) >> + for_each_cpu_and(i, policy->cpus, cpu_online_mask) >> __gov_queue_work(i, dbs_data, delay); >> } >> } > > Not required at all... policy->cpus is guaranteed to have only online cpus. Yeah, that's right, I guess the issue is, although the policy->cpus is correct at a given time, after get cpu from it, it's possible to be changed, unless we disabled preempt or irq, or hotplug before we use it... Like such issue cases: get x from policy->cpus DOWN notifier change policy->cpus do offline x send ipi to x Will that happen? Regards, Michael Wang > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >