From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753323Ab2GTRII (ORCPT ); Fri, 20 Jul 2012 13:08:08 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:33761 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753168Ab2GTRIG (ORCPT ); Fri, 20 Jul 2012 13:08:06 -0400 Date: Fri, 20 Jul 2012 10:08:02 -0700 From: Tejun Heo To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de, linux-pm@vger.kernel.org Subject: Re: [PATCHSET] workqueue: reimplement CPU hotplug to keep idle workers Message-ID: <20120720170802.GF32763@google.com> References: <1342545149-3515-1-git-send-email-tj@kernel.org> <1342802391.2583.11.camel@twins> <20120720165213.GD32763@google.com> <1342803700.2583.29.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1342803700.2583.29.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 Hello, Peter. On Fri, Jul 20, 2012 at 07:01:40PM +0200, Peter Zijlstra wrote: > On Fri, 2012-07-20 at 09:52 -0700, Tejun Heo wrote: > > Ooh, yeah, I agree. That's next on the wq to-do list. The problem is > > that queue_work() is implemented in terms of queue_work_on(). > > But that's trivial to fix, both could use __queue_work() without too > much bother, right? Hmmm? Not really. We need to keep count of the ones which reqested fixed binding - ie. the ones which explicitly used queue_work_on() - and then flush on wq CPU_DOWN. Then, we need to audit the current users which are using queue_work{_on}() + explicit FLUSH on CPU_DOWN and convert them. > > The assumption was that they should flush during CPU_DOWN but it > > probably will be much better to require users which need CPU affinity > > to always use queue_work_on() - instead of implicit local affinity > > from queue_work() - and flush them automatically from wq callback. > > Right, and when you create this new mode, which you need to know to > flush on DOWN, you can simply put a BUG_ON in queue_work_on() when this > mode is set. BUG_ON() on queue_work_on()? Do you mean if the target CPU is down? If so, yeah, I'd probably go with WARN_ON_ONCE() but we should whine on it. Thanks. -- tejun