Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751813Ab3JATFZ (ORCPT ); Tue, 1 Oct 2013 15:05:25 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:59233 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751251Ab3JATFX (ORCPT ); Tue, 1 Oct 2013 15:05:23 -0400 Date: Tue, 1 Oct 2013 12:05:15 -0700 From: "Paul E. McKenney" To: Oleg Nesterov Cc: Peter Zijlstra , "Srivatsa S. Bhat" , "Rafael J. Wysocki" , Mel Gorman , Rik van Riel , Srikar Dronamraju , Ingo Molnar , Andrea Arcangeli , Johannes Weiner , Linux-MM , LKML , Thomas Gleixner , Steven Rostedt , Viresh Kumar , tony.luck@intel.com, bp@alien8.de Subject: Re: [PATCH] hotplug: Optimize {get,put}_online_cpus() Message-ID: <20131001190515.GI5790@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20130925175055.GA25914@redhat.com> <20130928144720.GL15690@laptop.programming.kicks-ass.net> <20130928163104.GA23352@redhat.com> <7632387.20FXkuCITr@vostro.rjw.lan> <524B0233.8070203@linux.vnet.ibm.com> <20131001173615.GW3657@laptop.programming.kicks-ass.net> <20131001174508.GA17411@redhat.com> <20131001175640.GQ15690@laptop.programming.kicks-ass.net> <20131001180750.GA18261@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131001180750.GA18261@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13100119-6688-0000-0000-00000226938D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2174 Lines: 56 On Tue, Oct 01, 2013 at 08:07:50PM +0200, Oleg Nesterov wrote: > On 10/01, Peter Zijlstra wrote: > > > > On Tue, Oct 01, 2013 at 07:45:08PM +0200, Oleg Nesterov wrote: > > > > > > I tend to agree with Srivatsa... Without a strong reason it would be better > > > to preserve the current logic: "some time after" should not be after the > > > next CPU_DOWN/UP*. But I won't argue too much. > > > > Nah, I think breaking it is the right thing :-) > > I don't really agree but I won't argue ;) The authors of arch/x86/kernel/cpu/mcheck/mce.c would seem to be the guys who would need to complain, given that they seem to have the only use in 3.11. Thanx, Paul > > > But note that you do not strictly need this change. Just kill cpuhp_waitcount, > > > then we can change cpu_hotplug_begin/end to use xxx_enter/exit we discuss in > > > another thread, this should likely "join" all synchronize_sched's. > > > > That would still be 4k * sync_sched() == terribly long. > > No? the next xxx_enter() avoids sync_sched() if rcu callback is still > pending. Unless __cpufreq_remove_dev_finish() is "too slow" of course. > > > > Or split cpu_hotplug_begin() into 2 helpers which handle FAST -> SLOW and > > > SLOW -> BLOCK transitions, then move the first "FAST -> SLOW" handler outside > > > of for_each_online_cpu(). > > > > Right, that's more messy but would work if we cannot teach cpufreq (and > > possibly others) to not rely on state you shouldn't rely on anyway. > > Yes, > > > I tihnk the only guarnatee POST_DEAD should have is that it should be > > called before UP_PREPARE of the same cpu ;-) Nothing more, nothing less. > > See above... This makes POST_DEAD really "special" compared to other > CPU_* events. > > And again. Something like a global lock taken by CPU_DOWN_PREPARE and > released by POST_DEAD or DOWN_FAILED does not look "too wrong" to me. > > But I leave this to you and Srivatsa. > > Oleg. > -- 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/