From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933099Ab0JFU7k (ORCPT ); Wed, 6 Oct 2010 16:59:40 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:48218 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933085Ab0JFU7i (ORCPT ); Wed, 6 Oct 2010 16:59:38 -0400 Date: Wed, 6 Oct 2010 16:02:36 -0500 From: Sonny Rao To: Peter Zijlstra Cc: Nishanth Aravamudan , miltonm@bga.com, Thomas Gleixner , Ian Campbell , Peter P Waskiewicz Jr , linux-kernel@vger.kernel.org, sonnyrao@linux.vnet.ibm.com Subject: Re: [RESEND PATCH 1/2] IRQ: use cpu_possible_mask rather than online_mask in setup_affinity Message-ID: <20101006210236.GQ13726@us.ibm.com> References: <1285968378-12805-1-git-send-email-nacc@us.ibm.com> <1285968378-12805-2-git-send-email-nacc@us.ibm.com> <1286017262.2144.90.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1286017262.2144.90.camel@laptop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 02, 2010 at 01:01:02PM +0200, Peter Zijlstra wrote: > On Fri, 2010-10-01 at 14:26 -0700, Nishanth Aravamudan wrote: > > The use of online_mask requires architecture code to be hotplug-aware to > > account for IRQ round-robin'ing. > > Architectures that support hotplug should be hotplug aware, that's not > too much to ask imho. It seems like most architectures support HOTPLUG_CPU a quick grep for HOTPLUG_CPU in arch shows: arm blackfin ia64 m32r mips mn10300 parisc powerpc s390 sh sparc x86 also see my reply to Thomas -- it appears that many of the interrupt controller implementations enforce only affinitizing to online cpus The other point is, as this is generic code, it's making an assumption that online cpus is the right mask to test against and we know of at least one case where this isn't quite correct. > > With user-driven dynamic SMT, > > What's that? Well, that is basically a feature where we can use CPU hotplug to force a particular mode on an SMT (hardware multithreaded) processor The point here was really that on such multi-threaded processors -- which are becoming more common -- cpu hotplug can potentially be used fairly often. Sonny