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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6EE5C43334 for ; Thu, 21 Jul 2022 08:52:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232600AbiGUIwt (ORCPT ); Thu, 21 Jul 2022 04:52:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54530 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232592AbiGUIwo (ORCPT ); Thu, 21 Jul 2022 04:52:44 -0400 Received: from ZXSHCAS1.zhaoxin.com (ZXSHCAS1.zhaoxin.com [210.0.225.54]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 650B77E836; Thu, 21 Jul 2022 01:52:41 -0700 (PDT) Received: from zxbjmbx1.zhaoxin.com (10.29.252.163) by ZXSHCAS1.zhaoxin.com (10.28.252.161) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.27; Thu, 21 Jul 2022 16:52:14 +0800 Received: from [10.29.8.21] (10.29.8.21) by zxbjmbx1.zhaoxin.com (10.29.252.163) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.27; Thu, 21 Jul 2022 16:52:12 +0800 Message-ID: <154b2167-47f1-4d1e-0cd7-afab25033b76@zhaoxin.com> Date: Thu, 21 Jul 2022 16:52:11 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] USB: HCD: Fix URB giveback issue in tasklet function Content-Language: en-US To: Oliver Neukum , , , , , , , , , CC: , , , References: <20220721060833.4173-1-WeitaoWang-oc@zhaoxin.com> <09fed539-909a-f274-1a73-428dc7439d69@suse.com> From: "WeitaoWang-oc@zhaoxin.com" In-Reply-To: <09fed539-909a-f274-1a73-428dc7439d69@suse.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.29.8.21] X-ClientProxiedBy: ZXSHCAS1.zhaoxin.com (10.28.252.161) To zxbjmbx1.zhaoxin.com (10.29.252.163) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/7/21 16:00, Oliver Neukum wrote: > > > On 21.07.22 08:08, Weitao Wang wrote: >> Usb core introduce the mechanism of giveback of URB in tasklet context to >> reduce hardware interrupt handling time. On some test situation(such as >> FIO with 4KB block size), when tasklet callback function called to >> giveback URB, interrupt handler add URB node to the bh->head list also. >> If check bh->head list again after finish all URB giveback of local_list, >> then it may introduce a "dynamic balance" between giveback URB and add URB >> to bh->head list. This tasklet callback function may not exit for a long >> time, which will cause other tasklet function calls to be delayed. Some >> real-time applications(such as KB and Mouse) will see noticeable lag. >> > > Hi, > > ow do you know usb_hcd_giveback_urb() will be called in time to process > isoc URBs in time, if you leave them on the list? In fact how do > you be sure it will be called at all? I can see no upper time limit > on that. > > Regards > Oliver > > . If the bh->head list is not empty, patch method will raise a softirq immediately to call work function of every tasklet. Therefore, I think the left URB in bh->head list will be get giveback in time. Thanks weitao