From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422824AbaGRWxW (ORCPT ); Fri, 18 Jul 2014 18:53:22 -0400 Received: from mail-qg0-f45.google.com ([209.85.192.45]:39528 "EHLO mail-qg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762629AbaGRWxV (ORCPT ); Fri, 18 Jul 2014 18:53:21 -0400 Date: Fri, 18 Jul 2014 18:53:17 -0400 From: Tejun Heo To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] workqueue: remove unneeded test before wake up next worker Message-ID: <20140718225317.GC5739@htj.dyndns.org> References: <1405505409-12058-1-git-send-email-laijs@cn.fujitsu.com> <20140718220514.GC1819@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140718220514.GC1819@htj.dyndns.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 18, 2014 at 06:05:14PM -0400, Tejun Heo wrote: > On Wed, Jul 16, 2014 at 06:09:58PM +0800, Lai Jiangshan wrote: > > In this code: > > if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool)) > > wake_up_worker(pool); > > > > the first test is unneeded. Even the first test is removed, it doesn't affect > > the wake-up logic when WORKER_UNBOUND. And it will not introduce any useless > > wake-up when !WORKER_UNBOUND since the nr_running >= 1 except only one case. > > It will introduce useless/redundant wake-up when cpu_intensive, but this > > case is rare and next patch will also remove this redundant wake-up. > > > > Signed-off-by: Lai Jiangshan > > --- > > kernel/workqueue.c | 7 ++----- > > 1 files changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index f8d54c1..6d11b9a 100644 > > --- a/kernel/workqueue.c > > +++ b/kernel/workqueue.c > > @@ -2047,11 +2047,8 @@ __acquires(&pool->lock) > > if (unlikely(cpu_intensive)) > > worker_set_flags(worker, WORKER_CPU_INTENSIVE, true); > > > > - /* > > - * Unbound pool isn't concurrency managed and work items should be > > - * executed ASAP. Wake up another worker if necessary. > > - */ > > - if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool)) > > + /* Wake up another worker if necessary. */ > > + if (need_more_worker(pool)) > > wake_up_worker(pool); > > What does this buy us? Sure, it may achieve about the same operation > but it's a lot more confusing. need_more_worker() is specifically for > concurrency management. Applying it to unmanaged workers could lead > to okay behavior but conflating the two to save one test on worker > flags doesn't seem like a good trade-off to me. I take this back. We do guarantee that need_more_worker() returns %true for unbound pools and make use of that fact but I'd like it to retain the comment about unbound pools. Thanks. -- tejun