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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 9329CC04AB3 for ; Wed, 29 May 2019 08:41:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E81A21019 for ; Wed, 29 May 2019 08:41:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726186AbfE2Ilh (ORCPT ); Wed, 29 May 2019 04:41:37 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:17619 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725935AbfE2Ilg (ORCPT ); Wed, 29 May 2019 04:41:36 -0400 Received: from DGGEMS410-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 4C206269DD259F2AAC39; Wed, 29 May 2019 16:41:33 +0800 (CST) Received: from [127.0.0.1] (10.74.191.121) by DGGEMS410-HUB.china.huawei.com (10.3.19.210) with Microsoft SMTP Server id 14.3.439.0; Wed, 29 May 2019 16:41:26 +0800 Subject: Re: [PATCH net-next] net: link_watch: prevent starvation when processing linkwatch wq To: Salil Mehta , Stephen Hemminger CC: "davem@davemloft.net" , "hkallweit1@gmail.com" , "f.fainelli@gmail.com" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linuxarm References: <1558921674-158349-1-git-send-email-linyunsheng@huawei.com> <20190527075838.5a65abf9@hermes.lan> From: Yunsheng Lin Message-ID: Date: Wed, 29 May 2019 16:41:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.74.191.121] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/5/29 16:12, Salil Mehta wrote: >> From: netdev-owner@vger.kernel.org [mailto:netdev-owner@vger.kernel.org] On Behalf Of Yunsheng Lin >> Sent: Tuesday, May 28, 2019 2:04 AM >> >> On 2019/5/27 22:58, Stephen Hemminger wrote: >>> On Mon, 27 May 2019 09:47:54 +0800 >>> Yunsheng Lin wrote: >>> >>>> When user has configured a large number of virtual netdev, such >>>> as 4K vlans, the carrier on/off operation of the real netdev >>>> will also cause it's virtual netdev's link state to be processed >>>> in linkwatch. Currently, the processing is done in a work queue, >>>> which may cause worker starvation problem for other work queue. > > > I think we had already discussed about this internally and using separate > workqueue with WQ_UNBOUND should solve this problem. HNS3 driver was sharing > workqueue with the system workqueue. Yes, using WQ_UNBOUND wq in hns3 solved the cpu starvation for hns3 workqueue. But the rtnl_lock taken by linkwatch is still a problem for hns3's reset workqueue to do the down operation, which need a rtnl_lock. > > >>>> This patch releases the cpu when link watch worker has processed >>>> a fixed number of netdev' link watch event, and schedule the >>>> work queue again when there is still link watch event remaining. > > > We need proper examples/use-cases because of which we require above > kind of co-operative scheduling. Touching the common shared queue logic > which solid argument might invite for more problem to other modules. > > >>>> Signed-off-by: Yunsheng Lin >>> >>> Why not put link watch in its own workqueue so it is scheduled >>> separately from the system workqueue? >> >> From testing and debuging, the workqueue runs on the cpu where the >> workqueue is schedule when using normal workqueue, even using its >> own workqueue instead of system workqueue. So if the cpu is busy >> processing the linkwatch event, it is not able to process other >> workqueue' work when the workqueue is scheduled on the same cpu. >> >> Using unbound workqueue may solve the cpu starvation problem. > > [...] > >> But the __linkwatch_run_queue is called with rtnl_lock, so if it >> takes a lot time to process, other need to take the rtnl_lock may >> not be able to move forward. > > Please help me in understanding, Are you trying to pitch this patch > to solve more general system issue OR still your argument/concern > is related to the HNS3 driver problem mentioned in this patch? As about. > > Salil. > > > > > > >