From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755179AbdGSP0C (ORCPT ); Wed, 19 Jul 2017 11:26:02 -0400 Received: from mail-qt0-f196.google.com ([209.85.216.196]:36173 "EHLO mail-qt0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754233AbdGSP0B (ORCPT ); Wed, 19 Jul 2017 11:26:01 -0400 Date: Wed, 19 Jul 2017 11:25:57 -0400 From: Tejun Heo To: Christoph Hellwig Cc: Alexei Potashnik , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH wq/for-4.13-fixes] workqueue: restore WQ_UNBOUND/max_active==1 to be ordered Message-ID: <20170719152557.GL3365493@devbig577.frc2.facebook.com> References: <20170718191829.GA11583@infradead.org> <20170718224152.GJ3365493@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170718224152.GJ3365493@devbig577.frc2.facebook.com> 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 On Tue, Jul 18, 2017 at 06:41:52PM -0400, Tejun Heo wrote: > The combination of WQ_UNBOUND and max_active == 1 used to imply > ordered execution. After NUMA affinity 4c16bd327c74 ("workqueue: > implement NUMA affinity for unbound workqueues"), this is no longer > true due to per-node worker pools. > > While the right way to create an ordered workqueue is > alloc_ordered_workqueue(), the documentation has been misleading for a > long time and people do use WQ_UNBOUND and max_active == 1 for ordered > workqueues which can lead to subtle bugs which are very difficult to > trigger. > > It's unlikely that we'd see noticeable performance impact by enforcing > ordering on WQ_UNBOUND / max_active == 1 workqueues. Let's > automatically set __WQ_ORDERED for those workqueues. > > Signed-off-by: Tejun Heo > Reported-by: Christoph Hellwig > Reported-by: Alexei Potashnik > Fixes: 4c16bd327c74 ("workqueue: implement NUMA affinity for unbound workqueues") > Cc: stable@vger.kernel.org # v3.10+ Applied to wq/for-4.13-fixes. Thanks. -- tejun