Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757238Ab2FFQIo (ORCPT ); Wed, 6 Jun 2012 12:08:44 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:58049 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756937Ab2FFQIm (ORCPT ); Wed, 6 Jun 2012 12:08:42 -0400 Date: Wed, 6 Jun 2012 08:49:45 -0700 From: "Paul E. McKenney" To: Arjan van de Ven Cc: Peter Zijlstra , Thomas Gleixner , "Luck, Tony" , "Yu, Fenghua" , Rusty Russell , Ingo Molnar , H Peter Anvin , "Siddha, Suresh B" , "Mallick, Asit K" , linux-kernel , x86 , linux-pm , "Srivatsa S. Bhat" Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi Message-ID: <20120606154944.GL19601@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <3908561D78D1C84285E8C5FCA982C28F19300965@ORSMSX104.amr.corp.intel.com> <1338918625.2749.29.camel@twins> <1338925756.2749.36.camel@twins> <1338931856.2749.57.camel@twins> <20120605221240.GW2388@linux.vnet.ibm.com> <1338972223.2749.79.camel@twins> <20120606144127.GF19601@linux.vnet.ibm.com> <4FCF760A.7030501@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FCF760A.7030501@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12060616-7606-0000-0000-000000E8E924 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1923 Lines: 39 On Wed, Jun 06, 2012 at 08:23:54AM -0700, Arjan van de Ven wrote: > On 6/6/2012 7:41 AM, Paul E. McKenney wrote: > > On Wed, Jun 06, 2012 at 10:43:43AM +0200, Peter Zijlstra wrote: > >> On Tue, 2012-06-05 at 15:12 -0700, Paul E. McKenney wrote: > >>>> What I can't see is the isolated functional, aside from the above > >>>> mentioned things, that's not strictly a per-cpu property, we can have a > >>>> group that's isolated from the rest but not from each other. > >>> > >>> I suspect that Thomas is thinking that the CPU is so idle that it no > >>> longer has to participate in TLB invalidation or RCU. (Thomas will > >>> correct me if I am confused.) But Peter, is that the level of idle > >>> you are thinking of? > >> > >> No, we're talking about isolated, so its very much running something. > > > > From what I can see, if the CPU is running something, this is Thomas's > > "Isolated functional" state rather than his "Isolated idle" state. > > The isolated-idle state should not need to participate in TLB invalidation > > or RCU, so that the CPU never ever needs to wake up while in the > > isolated-idle state. > > btw TLB invalidation I think is a red herring in this discussion > (other than "global PTEs" kind of kernel pte changes); > at least on x86 this is not happening for a long time; if a CPU is > really idle (which means the CPU internally flushes the tlbs anyway), > Linux also switches to the kernel PTE set so there's no need for a flush > later on. Right, as I understand it, only unmappings in the kernel address space would need to IPI an idle CPU. But this is still a source of IPIs that could wake up the CPU, correct? Thanx, Paul -- 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/