From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757133Ab0EXPRR (ORCPT ); Mon, 24 May 2010 11:17:17 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:53111 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753696Ab0EXPRQ (ORCPT ); Mon, 24 May 2010 11:17:16 -0400 Date: Mon, 24 May 2010 20:46:55 +0530 From: Srivatsa Vaddagiri To: Peter Zijlstra Cc: "Amit K. Arora" , tj@kernel.org, Ingo Molnar , Gautham R Shenoy , Darren Hart , Brian King , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Make sure timers have migrated before killing migration_thread Message-ID: <20100524151655.GF13808@linux.vnet.ibm.com> Reply-To: vatsa@in.ibm.com References: <20100519090557.GA15237@amitarora.in.ibm.com> <1274261515.5605.10423.camel@twins> <20100524095951.GA17680@amitarora.in.ibm.com> <1274707726.5605.31932.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1274707726.5605.31932.camel@twins> 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 Mon, May 24, 2010 at 03:28:45PM +0200, Peter Zijlstra wrote: > On Mon, 2010-05-24 at 15:29 +0530, Amit K. Arora wrote: > > since _cpu_up() and _cpu_down() can never run in > > parallel, because of cpu_add_remove_lock. > > Ah indeed. I guess your initial patch works then. One thing I found surprising was that a cpu's rt-bandwidth renewal could be dependant on another cpu's (rt-bandwidth) timer firing ontime. In this case, we had migration/23 pulled over to CPU0 and we hung later waiting for migration/23 to exit. migration/23 was not exiting because it could not run on CPU0 (as CPU0's rt-bandwidth had expired). This situation remained forever. I would have expected CPU0's bandwidth to have been renewed independent of some timer on CPU23 to fire - maybe I am missing something not obvious in the code? - vatsa