Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756592Ab2FOJ6Q (ORCPT ); Fri, 15 Jun 2012 05:58:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:37498 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756208Ab2FOJ6P convert rfc822-to-8bit (ORCPT ); Fri, 15 Jun 2012 05:58:15 -0400 Message-ID: <1339754286.2559.48.camel@twins> Subject: Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads From: Peter Zijlstra To: Tejun Heo Cc: Thomas Gleixner , "Paul E. McKenney" , LKML , Ingo Molnar , "Srivatsa S. Bhat" , Rusty Russell Date: Fri, 15 Jun 2012 11:58:06 +0200 In-Reply-To: <20120615015331.GC12624@mtj.dyndns.org> References: <20120613102823.373180763@linutronix.de> <20120613105815.206105518@linutronix.de> <20120613183301.GE2427@linux.vnet.ibm.com> <1339661331.2559.5.camel@twins> <1339661848.2559.7.camel@twins> <20120615015331.GC12624@mtj.dyndns.org> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1664 Lines: 42 On Fri, 2012-06-15 at 10:53 +0900, Tejun Heo wrote: > On Thu, Jun 14, 2012 at 10:17:28AM +0200, Peter Zijlstra wrote: > > On Thu, 2012-06-14 at 10:08 +0200, Peter Zijlstra wrote: > > > On Wed, 2012-06-13 at 20:56 +0200, Thomas Gleixner wrote: > > > > If it's just a spurious wakeup then it goes back to sleep right away > > > > as nothing cleared the park bit. > > > > > > Your spurious wakeup will have destroyed the binding though. So you need > > > to be careful. > > > > We should probably do something like the below.. > > > > TJ does this wreck workqueues? Its somewhat 'creative' in that regard > > and really wants fixing. > > > > --- > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -5018,6 +5018,8 @@ void do_set_cpus_allowed(struct task_str > > > > cpumask_copy(&p->cpus_allowed, new_mask); > > p->nr_cpus_allowed = cpumask_weight(new_mask); > > + if (p->nr_cpus_allowed != 1) > > + p->flags &= ~PF_THREAD_BOUND; > > The only reason wq workers use PF_THREAD_BOUND is to prevent userland > from mucking with cpus_allowed, so the above wouldn't break anything > in itself although userland would be able to wreck it afterwards. Thing is, if things could get wrecked by userland moving a thread to a different cpu, things just got wrecked by the kernel doing that very same thing. PF_THREAD_BOUND isn't called PF_NO_USER_AFFINITY (although it seems a popular interpretation). -- 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/