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 EDE1AC04AB3 for ; Tue, 28 May 2019 01:48:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C042220823 for ; Tue, 28 May 2019 01:48:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727844AbfE1Bse (ORCPT ); Mon, 27 May 2019 21:48:34 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:17583 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727271AbfE1Bse (ORCPT ); Mon, 27 May 2019 21:48:34 -0400 Received: from DGGEMS411-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 560C66BA30B9C8FF9BBD; Tue, 28 May 2019 09:48:32 +0800 (CST) Received: from [127.0.0.1] (10.74.191.121) by DGGEMS411-HUB.china.huawei.com (10.3.19.211) with Microsoft SMTP Server id 14.3.439.0; Tue, 28 May 2019 09:48:22 +0800 Subject: Re: [PATCH net-next] net: link_watch: prevent starvation when processing linkwatch wq To: Stephen Hemminger CC: , , , , , References: <1558921674-158349-1-git-send-email-linyunsheng@huawei.com> <20190527075838.5a65abf9@hermes.lan> <20190527181744.289c4b2f@hermes.lan> From: Yunsheng Lin Message-ID: Date: Tue, 28 May 2019 09:48:22 +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: <20190527181744.289c4b2f@hermes.lan> 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 2019/5/28 9:17, Stephen Hemminger wrote: > On Tue, 28 May 2019 09:04:18 +0800 > Yunsheng Lin wrote: > >> 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. >>>> >>>> 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. >>>> >>>> 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. > > Agree with the starvation issue. My cocern is that large number of > events that end up being delayed would impact things that are actually > watching for link events (like routing daemons). Agreed. I am not familiar with above use cases, it would be very helpful if someone can help testing the impact of above use case. > > It probably would be not accepted to do rtnl_unlock/sched_yield/rtnl_lock > in the loop, but that is another alternative. Yes. But seems not very efficient to do rtnl_unlock/sched_yield/rtnl_lock for very linkwatch_do_dev. > > > > . >