From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757192AbcGZPe0 (ORCPT ); Tue, 26 Jul 2016 11:34:26 -0400 Received: from mail-qk0-f193.google.com ([209.85.220.193]:34173 "EHLO mail-qk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755107AbcGZPeZ (ORCPT ); Tue, 26 Jul 2016 11:34:25 -0400 Date: Tue, 26 Jul 2016 11:34:21 -0400 From: Tejun Heo To: Bhaktipriya Shridhar Cc: Greg Kroah-Hartman , Saurabh Karajgaonkar , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] usb: ftdi-elan: Remove deprecated create_singlethread_workqueue Message-ID: <20160726153421.GP19588@mtj.duckdns.org> References: <20160726051720.GA14875@Karyakshetra> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160726051720.GA14875@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 10:47:20AM +0530, Bhaktipriya Shridhar wrote: > The status workqueue is involved in initializing the Uxxx and polling > the Uxxx until a supported PCMCIA CardBus device is detected. > It then starts the command and respond workqueues and then loads the > module that handles the device, after which it just polls the Uxxx > looking for card ejects. > > The command and respond workqueues are involved in implementing a command > sequencer for communicating with the firmware on the other side of > the FTDI chip in the Uxxx. > > These workqueues have only a single work item each and hence they do not > require ordering. Also, none of the above workqueues are being used on a > memory recliam path. Hence, the singlethreaded workqueues have 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 items have been sync cancelled because they are self-requeueing > and need to wait for the in-flight work item to finish before proceeding > with destruction. Hence, they have been sync cancelled in > ftdi_status_cancel_work(), ftdi_command_cancel_work() and > ftdi_response_cancel_work(). These functions are called in > ftdi_elan_exit() to ensure that there are no pending work items while > disconnecting the driver. > > Signed-off-by: Bhaktipriya Shridhar Acked-by: Tejun Heo Thanks. -- tejun