From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4BE9C433DF for ; Mon, 17 Aug 2020 19:41:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D93F20674 for ; Mon, 17 Aug 2020 19:41:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404307AbgHQTlk (ORCPT ); Mon, 17 Aug 2020 15:41:40 -0400 Received: from netrider.rowland.org ([192.131.102.5]:58775 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729708AbgHQPZN (ORCPT ); Mon, 17 Aug 2020 11:25:13 -0400 Received: (qmail 113589 invoked by uid 1000); 17 Aug 2020 11:25:07 -0400 Date: Mon, 17 Aug 2020 11:25:07 -0400 From: Alan Stern To: Jim Baxter Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-usb@vger.kernel.org, "Resch Carsten \(CM/ESO6\)" , "Rosca, Eugeniu \(ADITG/ESB\)" Subject: Re: PROBLEM: Long Workqueue delays. Message-ID: <20200817152507.GC112820@rowland.harvard.edu> References: <71aafe68-7fe0-6b77-ea8e-83edd3f16c8d@mentor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <71aafe68-7fe0-6b77-ea8e-83edd3f16c8d@mentor.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 17, 2020 at 12:40:03PM +0100, Jim Baxter wrote: > We have issues with the workqueue of the kernel overloading the CPU 0 > when we we disconnect a USB stick. Do you unmount the stick before disconnecting it? > This results in other items on the shared workqueue being delayed by > around 6.5 seconds with a default kernel configuration and 2.3 seconds > on a config tailored for our RCar embedded platform. > > I am aware there will be delays on the shared workqueue, are the delays > we are seeing considered normal? Assuming the workqueue delay is caused by the USB subsystem, you may be able to get more information by turning on USB dynamic debugging: echo 'module usbcore =p' >/sys/kernel/debug/dynamic_debug/control and seeing what shows up in the dmesg log. One long-running job should not normally be enough to delay an entire workqueues. Workqueues are allowed to spawn multiple threads; they are supposed to resize themselves dynamically as required. Alan Stern