From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752374Ab2IRRIK (ORCPT ); Tue, 18 Sep 2012 13:08:10 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:59043 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751386Ab2IRRIH (ORCPT ); Tue, 18 Sep 2012 13:08:07 -0400 Date: Tue, 18 Sep 2012 10:08:02 -0700 From: Tejun Heo To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] workqueue: Keep activate-order equals to queue_work()-order Message-ID: <20120918170802.GC8474@google.com> References: <1347957414-6692-1-git-send-email-laijs@cn.fujitsu.com> <1347957414-6692-2-git-send-email-laijs@cn.fujitsu.com> <20120918170519.GB8474@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120918170519.GB8474@google.com> 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 Tue, Sep 18, 2012 at 10:05:19AM -0700, Tejun Heo wrote: > On Tue, Sep 18, 2012 at 04:36:53PM +0800, Lai Jiangshan wrote: > > The whole workqueue.c keeps activate-order equals to queue_work()-order > > in any given cwq except workqueue_set_max_active(). > > > > If this order is not kept, something may be not good: > > > > first_work_fn() { release some resource; } > > second_work_fn() { wait and request the resource; use resource; } > > > > 1. user queues the first work. # ->max_active is low, is queued on ->delayed_works. > > 2. someone increases the >max_active via workqueue_set_max_active() > > 3. user queues the second work. # queued on cwq->pool. > > > > When the second work is launched to execute, it waits the first work > > to release the resource. But the first work is still in ->delayed_works, > > it waits the first work to finish and them it can be activated. > > > > It is bad. we fix it by activating the first work in the step 2. > > > > I can't fully determine that it is workqueue's responsibility > > or the user's responsibility. > > If it is workqueue's responsibility, the patch needs go to -stable. > > If it is user's responsibility. it is a nice cleanup, it can go to for-next. > > I prefer it is workqueue's responsibility. > > Unless max_active == 1, workqueue doesn't give any guarantee on > execution order. I don't think we need to care about this. That said, I kinda like the patches. Can you please update the description on the second patch to something along the line of "use common set_max_active logic which immediately makes use of the newly increased max_mactive if there are delayed work items and also happens to keep activation ordering"? Thanks. -- tejun