From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756290Ab0EDHSN (ORCPT ); Tue, 4 May 2010 03:18:13 -0400 Received: from hera.kernel.org ([140.211.167.34]:40837 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751923Ab0EDHSM (ORCPT ); Tue, 4 May 2010 03:18:12 -0400 Message-ID: <4BDFC9FB.4020607@kernel.org> Date: Tue, 04 May 2010 09:17:15 +0200 From: Tejun Heo User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4 MIME-Version: 1.0 To: Peter Zijlstra CC: mingo@elte.hu, linux-kernel@vger.kernel.org, x86@kernel.org, oleg@redhat.com, rusty@rustcorp.com.au, sivanich@sgi.com, heiko.carstens@de.ibm.com, dipankar@in.ibm.com, josh@freedesktop.org, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, arjan@linux.intel.com, torvalds@linux-foundation.org Subject: Re: [PATCH 3/4] scheduler: replace migration_thread with cpu_stop References: <1271952554-22368-1-git-send-email-tj@kernel.org> <1271952554-22368-4-git-send-email-tj@kernel.org> <1272893192.5605.122.camel@twins> In-Reply-To: <1272893192.5605.122.camel@twins> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Tue, 04 May 2010 07:17:17 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On 05/03/2010 03:26 PM, Peter Zijlstra wrote: > On Thu, 2010-04-22 at 18:09 +0200, Tejun Heo wrote: >> @@ -2909,7 +2912,9 @@ redo: >> } >> raw_spin_unlock_irqrestore(&busiest->lock, flags); >> if (active_balance) >> - wake_up_process(busiest->migration_thread); >> + stop_one_cpu_nowait(cpu_of(busiest), >> + active_load_balance_cpu_stop, busiest, >> + &busiest->active_balance_work); > > So who guarantees busiest->active_balance_work isn't already enqueued by > some other cpu's load-balancer run? > Hmmm... maybe I'm mistaken but isn't that guaranteed by busiest->active_balance which is protected by the rq lock? active_load_balance_cpu_stop is scheduled iff busiest->active_balance was changed from zero and only active_load_balance_cpu_stop() can clear it at the end of its execution at which point the active_balance_work is safe to reuse. Thanks. -- tejun