From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932097AbcGZQvm (ORCPT ); Tue, 26 Jul 2016 12:51:42 -0400 Received: from mail-yw0-f194.google.com ([209.85.161.194]:33248 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757170AbcGZQvg (ORCPT ); Tue, 26 Jul 2016 12:51:36 -0400 Date: Tue, 26 Jul 2016 12:51:34 -0400 From: Tejun Heo To: Bhaktipriya Shridhar Cc: Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] USB: appledisplay: Remove deprecated create_singlethread_workqueue Message-ID: <20160726165134.GV19588@mtj.duckdns.org> References: <20160726164918.GA6234@Karyakshetra> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160726164918.GA6234@Karyakshetra> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 26, 2016 at 10:19:18PM +0530, Bhaktipriya Shridhar wrote: > The workqueue "wq" is involved in controlling the brightness of an > Apple Cinema Display over USB. > > It has a single work item(&pdata->work) per appledisplay and hence > doesn't require ordering. Also, it is not being used on a memory > reclaim path. > > Hence, the singlethreaded workqueue has been replaced with the use of > system_wq. > > System workqueues have been able to handle high level of concurrency > for a long time now and hence it's not required to have a singlethreaded > workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue > created with create_singlethread_workqueue(), system_wq allows multiple > work items to overlap executions even on the same CPU; however, a > per-cpu workqueue doesn't have any CPU locality or global ordering > guarantee unless the target CPU is explicitly specified and thus the > increase of local concurrency shouldn't make any difference. > > The work item is self-requeueing and needs to wait for the in-flight > work item to finish before proceeding with destruction. > Hence, it has been sync cancelled in appledisplay_disconnect(). > This also ensures that there are no pending tasks while disconnecting > the driver. > > Signed-off-by: Bhaktipriya Shridhar Acked-by: Tejun Heo Thanks. -- tejun