From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755508AbZHUAVh (ORCPT ); Thu, 20 Aug 2009 20:21:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932122AbZHUAVg (ORCPT ); Thu, 20 Aug 2009 20:21:36 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:32851 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755311AbZHUAVf (ORCPT ); Thu, 20 Aug 2009 20:21:35 -0400 Date: Thu, 20 Aug 2009 17:20:27 -0700 From: Andrew Morton To: Jens Axboe Cc: linux-kernel@vger.kernel.org, jeff@garzik.org, benh@kernel.crashing.org, htejun@gmail.com, bzolnier@gmail.com, alan@lxorguk.ukuu.org.uk, jens.axboe@oracle.com Subject: Re: [PATCH 2/6] workqueue: add support for lazy workqueues Message-Id: <20090820172027.cdc41d1e.akpm@linux-foundation.org> In-Reply-To: <1250763466-24282-5-git-send-email-jens.axboe@oracle.com> References: <1250763466-24282-1-git-send-email-jens.axboe@oracle.com> <1250763466-24282-2-git-send-email-jens.axboe@oracle.com> <1250763466-24282-3-git-send-email-jens.axboe@oracle.com> <1250763466-24282-4-git-send-email-jens.axboe@oracle.com> <1250763466-24282-5-git-send-email-jens.axboe@oracle.com> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 20 Aug 2009 12:17:39 +0200 Jens Axboe wrote: > Lazy workqueues are like normal workqueues, except they don't > start a thread per CPU by default. Instead threads are started > when they are needed, and exit when they have been idle for > some time. > > > ... > > @@ -280,7 +309,34 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq) > trace_workqueue_execution(cwq->thread, work); > cwq->current_work = work; > list_del_init(cwq->worklist.next); > + cpu = smp_processor_id(); > spin_unlock_irq(&cwq->lock); > + did_work = 1; > + > + /* > + * If work->cpu isn't us, then we need to create the target > + * workqueue thread (if someone didn't already do that) and > + * move the work over there. > + */ > + if ((cwq->wq->flags & WQ_F_LAZY) && work->cpu != cpu) { > + struct cpu_workqueue_struct *__cwq; > + struct task_struct *p; > + int err; > + > + __cwq = wq_per_cpu(cwq->wq, work->cpu); > + p = __cwq->thread; > + if (!p) > + err = create_workqueue_thread(__cwq, work->cpu); > + p = __cwq->thread; > + if (p) { > + if (work->cpu >= 0) It's an unsigned int. This test is always true. > + kthread_bind(p, work->cpu); I wonder what happens if work->cpu isn't online any more. > + insert_work(__cwq, work, &__cwq->worklist); > + wake_up_process(p); > + goto out; > + } > + } > + > > BUG_ON(get_wq_data(work) != cwq); > work_clear_pending(work); > > ... >