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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 6A4B9C282DC for ; Mon, 3 Jun 2019 01:20:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 38599278F8 for ; Mon, 3 Jun 2019 01:20:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726820AbfFCBUO (ORCPT ); Sun, 2 Jun 2019 21:20:14 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:17645 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726305AbfFCBUO (ORCPT ); Sun, 2 Jun 2019 21:20:14 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 507545137AFE3F29BA21; Mon, 3 Jun 2019 09:20:11 +0800 (CST) Received: from [127.0.0.1] (10.74.191.121) by DGGEMS402-HUB.china.huawei.com (10.3.19.202) with Microsoft SMTP Server id 14.3.439.0; Mon, 3 Jun 2019 09:20:00 +0800 Subject: Re: [PATCH v2 net-next] net: link_watch: prevent starvation when processing linkwatch wq To: Salil Mehta , "davem@davemloft.net" CC: "hkallweit1@gmail.com" , "f.fainelli@gmail.com" , "stephen@networkplumber.org" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Linuxarm References: <1559293233-43017-1-git-send-email-linyunsheng@huawei.com> <0500aaf60c464528b6bae010c7f9994d@huawei.com> From: Yunsheng Lin Message-ID: <802fef29-d525-2559-f2fc-d88ac3193f06@huawei.com> Date: Mon, 3 Jun 2019 09:20:00 +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: <0500aaf60c464528b6bae010c7f9994d@huawei.com> 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 2019/5/31 17:54, Salil Mehta wrote: >> From: netdev-owner@vger.kernel.org On Behalf Of Yunsheng Lin >> Sent: Friday, May 31, 2019 10:01 AM >> To: davem@davemloft.net >> Cc: hkallweit1@gmail.com; f.fainelli@gmail.com; >> stephen@networkplumber.org; netdev@vger.kernel.org; linux- >> kernel@vger.kernel.org; Linuxarm >> Subject: [PATCH v2 net-next] net: link_watch: prevent starvation when >> processing linkwatch wq >> >> 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 cpu and rtnl locking starvation problem. >> >> This patch releases the cpu and rtnl lock when link watch worker >> has processed a fixed number of netdev' link watch event. >> >> Currently __linkwatch_run_queue is called with rtnl lock, so >> enfore it with ASSERT_RTNL(); > > > Typo enfore --> enforce ? My mistake. thanks. > > > >> Signed-off-by: Yunsheng Lin >> --- >> V2: use cond_resched and rtnl_unlock after processing a fixed >> number of events >> --- >> net/core/link_watch.c | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/net/core/link_watch.c b/net/core/link_watch.c >> index 7f51efb..07eebfb 100644 >> --- a/net/core/link_watch.c >> +++ b/net/core/link_watch.c >> @@ -168,9 +168,18 @@ static void linkwatch_do_dev(struct net_device >> *dev) >> >> static void __linkwatch_run_queue(int urgent_only) >> { >> +#define MAX_DO_DEV_PER_LOOP 100 >> + >> + int do_dev = MAX_DO_DEV_PER_LOOP; >> struct net_device *dev; >> LIST_HEAD(wrk); >> >> + ASSERT_RTNL(); >> + >> + /* Give urgent case more budget */ >> + if (urgent_only) >> + do_dev += MAX_DO_DEV_PER_LOOP; >> + >> /* >> * Limit the number of linkwatch events to one >> * per second so that a runaway driver does not >> @@ -200,6 +209,14 @@ static void __linkwatch_run_queue(int urgent_only) >> } >> spin_unlock_irq(&lweventlist_lock); >> linkwatch_do_dev(dev); >> + > > > A comment like below would be helpful in explaining the reason of the code. > > /* This function is called with rtnl_lock held. If excessive events > * are present as part of the watch list, their processing could > * monopolize the rtnl_lock and which could lead to starvation in > * other modules which want to acquire this lock. Hence, co-operative > * scheme like below might be helpful in mitigating the problem. > * This also tries to be fair CPU wise by conditional rescheduling. > */ Yes, thanks for the helpful comment. > > >> + if (--do_dev < 0) { >> + rtnl_unlock(); >> + cond_resched(); >> + do_dev = MAX_DO_DEV_PER_LOOP; >> + rtnl_lock(); >> + } >> + >> spin_lock_irq(&lweventlist_lock); >> } > > . >