Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757555Ab1EMHbs (ORCPT ); Fri, 13 May 2011 03:31:48 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:58392 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754558Ab1EMHbr (ORCPT ); Fri, 13 May 2011 03:31:47 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Message-ID: <4DCCDEC5.3040201@jp.fujitsu.com> Date: Fri, 13 May 2011 16:33:25 +0900 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; ja; rv:1.9.2.17) Gecko/20110414 Lightning/1.0b2 Thunderbird/3.1.10 MIME-Version: 1.0 To: Yong Zhang CC: Peter Zijlstra , Oleg Nesterov , LKML , Andrew Morton , Ingo Molnar , Li Zefan , Miao Xie Subject: Re: [PATCH 1/2] cpuset: fix cpuset_cpus_allowed_fallback() don't update tsk->rt.nr_cpus_allowed References: <20110428161149.GA15658@redhat.com> <20110502194416.2D61.A69D9226@jp.fujitsu.com> <20110502195657.2D68.A69D9226@jp.fujitsu.com> <1305129929.2914.247.camel@laptop> <4DCCC61F.80408@jp.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1858 Lines: 51 Hello, >>>> (3) schedule() makes fallback and cpuset_cpus_allowed_fallback >>>> change task->cpus_allowed >>> >>> I'm failing to see how this is happening, surely that kthread isn't >>> actually running that early? >> >> If my understand correctly, current call graph is below. >> >> kernel_init() >> smp_init(); >> cpu_up() >> ... cpu hotplug notification >> kthread_create() >> sched_init_smp(); >> >> >> So, cpu hotplug event is happen before sched_init_smp(). The old rule is, >> all kthreads of using cpu-up notification have to use kthread_bind(). It >> protected from sched load balance. >> >> but, now cpuset_cpus_allowed_fallback() forcedly change kthread's cpumask. >> Why is this works? the point are two. >> >> - rcu_cpu_kthread_should_stop() call set_cpus_allowed_ptr() again >> periodically. >> then, it can reset cpumask if cpuset_cpus_allowed_fallback() change it. >> my debug print obseve following cpumask change occur at boot time. >> 1) kthread_bind: bind cpu1 >> 2) cpuset_cpus_allowed_fallback: bind possible cpu >> 3) rcu_cpu_kthread_should_stop: rebind cpu1 >> - while tsk->rt.nr_cpus_allowed == 1, sched load balancer never be crash. > > Seems rcu_spawn_one_cpu_kthread() call wake_up_process() directly, > which is under hotplug event CPU_UP_PREPARE. Maybe it should be > under CPU_ONLINE. Hmm.. I haven't catch your point. cpu_up() call both CPU_UP_PREPARE and CPU_ONLINE notification. Thus, CPU_ONLINE still be called before sched_init_smp(). Am I missing something? -- 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/