From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758148Ab1I3IJZ (ORCPT ); Fri, 30 Sep 2011 04:09:25 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:51906 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755418Ab1I3IJS (ORCPT ); Fri, 30 Sep 2011 04:09:18 -0400 Date: Fri, 30 Sep 2011 01:09:14 -0700 From: Tejun Heo To: Gilad Ben-Yossef Cc: Ripduman Sohan , linux-kernel@vger.kernel.org, peterz@infradead.org Subject: Re: [PATCH] workqueue: Restore cpus_allowed mask for sleeping workqueue rescue threads Message-ID: <20110930080914.GM10425@mtj.dyndns.org> References: <1314884193-20454-1-git-send-email-ripduman.sohan@cl.cam.ac.uk> <20110902002917.GD2752@htj.dyndns.org> <20110915161430.GE1548@tusker> <20110924030718.GA29319@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Sun, Sep 25, 2011 at 09:02:25AM +0300, Gilad Ben-Yossef wrote: > Thank you for taking the time to answer my query :-) > > I agree there is no real problem with having an additional task > bound to an "isolated" CPU so long that it does not run and of > course that if a task on an isolated CPU initiated activity that > resulted in requiring the services of a rescuer workqueue thread it > most certainly needs to run there and that is fine. > > I guess my question is - apart form running on the isolated CPU, > does the fact that the rescuer thread is bound there can cause > activity on that CPU originating from a foreign CPU, such as for > example running an IPI handler in order to migrate it there? Hmmm... indeed. This can cause an unnecessary wakeup / migration on an isolated CPU when another CPU asks for the rescuer, so yeah it makes sense to change the behavior. BTW, why didn't the original patch simply use set_cpus_allowed_ptr(cpu_all_mask)? Thanks. -- tejun