From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753862AbYIAFAX (ORCPT ); Mon, 1 Sep 2008 01:00:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750970AbYIAFAK (ORCPT ); Mon, 1 Sep 2008 01:00:10 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:41633 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750753AbYIAFAJ (ORCPT ); Mon, 1 Sep 2008 01:00:09 -0400 Date: Sun, 31 Aug 2008 22:00:04 -0700 From: "Paul E. McKenney" To: Benjamin Herrenschmidt Cc: linux-kernel@vger.kernel.org, paulus@samba.org, jwboyer@linux.vnet.ibm.com, tnt@246tNt.com, grant.likely@secretlab.ca, linuxppc-dev@ozlabs.org, manfred@colorfullife.com, akpm@linux-foundation.org Subject: Re: [PATCH] prevent powerpc from invoking irq handlers on offline CPUs Message-ID: <20080901050003.GN7015@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20080831173127.GA15296@linux.vnet.ibm.com> <1220229284.13162.411.camel@pasglop> <20080901020640.GM7015@linux.vnet.ibm.com> <1220238880.13010.4.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1220238880.13010.4.camel@pasglop> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 01, 2008 at 01:14:40PM +1000, Benjamin Herrenschmidt wrote: > On Sun, 2008-08-31 at 19:06 -0700, Paul E. McKenney wrote: > > On Mon, Sep 01, 2008 at 10:34:44AM +1000, Benjamin Herrenschmidt wrote: > > > On Sun, 2008-08-31 at 10:31 -0700, Paul E. McKenney wrote: > > > > Make powerpc refrain from clearing a given to-be-offlined CPU's bit in the > > > > cpu_online_mask until it has processed pending irqs. This change > > > > prevents other CPUs from being blindsided by an apparently offline CPU > > > > nevertheless changing globally visible state. > > > > > > > > Signed-off-by: Paul E. McKenney > > > > --- > > > > > > Sounds reasonable... the only possible worry here is if somebody tries > > > an IPI ... The IPI code will and the target CPU mask with the online > > > map, so it may try to send to the to-be-offlined CPU and timeout, no ? > > > > OK. Do we need separate IPI and online masks? > > Shouldn't we already have routed all interrupts to other CPUs anyway ? > > IE. The affinity of all interrupts should have been updated. So the > only thing we're going to get here are possibly IPIs and decrementer, > I don't see it being a big deal making sure we test we are online when > receiving it. It did look to me that the CPU removed itself from the interrupt queue before re-enabling interrupts, so makes sense to me... Thanx, Paul