From patchwork Thu Sep 17 23:49:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Francesco Ruggeri X-Patchwork-Id: 260688 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=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 4C707C43465 for ; Thu, 17 Sep 2020 23:49:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F1F6208B8 for ; Thu, 17 Sep 2020 23:49:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="1YdG9jLl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726134AbgIQXty (ORCPT ); Thu, 17 Sep 2020 19:49:54 -0400 Received: from mx.aristanetworks.com ([162.210.129.12]:37114 "EHLO smtp.aristanetworks.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725886AbgIQXty (ORCPT ); Thu, 17 Sep 2020 19:49:54 -0400 Received: from us180.sjc.aristanetworks.com (us180.sjc.aristanetworks.com [10.243.128.7]) by smtp.aristanetworks.com (Postfix) with ESMTP id E53F0402CF6; Thu, 17 Sep 2020 16:49:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=Arista-A; t=1600386593; bh=3mGeEJtfpy/OYgDYPcjZMbm1NYXeXX6f8ds3K0JrI0Y=; h=Date:To:Subject:From:From; b=1YdG9jLlZA2OFGLtwHTY0x1Rmo2WvWtLLqc3zqGSisVBBHF6+B1vucCmaxbqxAUPy x0Hk7xwQvhhVMx2XE/3eSeGnJT+MB6WaXOsXxQ+gcagOKnkQV6x9dH6Vaz3OVrLNy8 nFbf7SrhkXxVMY8aiFUnEFlj0UqnaerltpSbZxd7VGAhDc0yLsbzVuMxeSIKPAWE9T WzjO1Pi3/V/qlQMikinyvkUGAVh1zOtoLq8/Bp77SFnV9THszv/Qofch6m3jPVYGH4 MYweUOOJ8JYnYnVVgFg0SQSZsVChrqHigrZg7ZuiwZXAZ9FcJ+b4JBAGv5CquAVTjw lP4xhA02dQWCg== Received: by us180.sjc.aristanetworks.com (Postfix, from userid 10189) id CB1D295C0A69; Thu, 17 Sep 2020 16:49:53 -0700 (PDT) Date: Thu, 17 Sep 2020 16:49:53 -0700 To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, xiyou.wangcong@gmail.com, ap420073@gmail.com, andriin@fb.com, edumazet@google.com, jiri@mellanox.com, ast@kernel.org, kuba@kernel.org, davem@davemloft.net, fruggeri@arista.com Subject: [PATCH v3] net: use exponential backoff in netdev_wait_allrefs User-Agent: Heirloom mailx 12.5 7/5/10 Message-Id: <20200917234953.CB1D295C0A69@us180.sjc.aristanetworks.com> From: fruggeri@arista.com (Francesco Ruggeri) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The combination of aca_free_rcu, introduced in commit 2384d02520ff ("net/ipv6: Add anycast addresses to a global hashtable"), and fib6_info_destroy_rcu, introduced in commit 9b0a8da8c4c6 ("net/ipv6: respect rcu grace period before freeing fib6_info"), can result in an extra rcu grace period being needed when deleting an interface, with the result that netdev_wait_allrefs ends up hitting the msleep(250), which is considerably longer than the required grace period. This can result in long delays when deleting a large number of interfaces, and it can be observed with this script: ns=dummy-ns NIFS=100 ip netns add $ns ip netns exec $ns ip link set lo up ip netns exec $ns sysctl net.ipv6.conf.default.disable_ipv6=0 ip netns exec $ns sysctl net.ipv6.conf.default.forwarding=1 for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link add $if type dummy ip netns exec $ns ip link set $if up ip netns exec $ns ip -6 addr add 2021:$i::1/120 dev $if done for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link del $if done ip netns del $ns This patch uses exponential backoff instead of the fixed msleep(250) to get out of the loop faster. Time with this patch on a 5.4 kernel: real 0m8.199s user 0m0.402s sys 0m1.213s Time without this patch: real 0m31.522s user 0m0.438s sys 0m1.156s v2: use exponential backoff instead of trying to wake up netdev_wait_allrefs. v3: preserve reverse christmas tree ordering of local variables Signed-off-by: Francesco Ruggeri --- net/core/dev.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index 4086d335978c..e5fa60cb8832 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -9986,9 +9986,12 @@ EXPORT_SYMBOL(netdev_refcnt_read); * We can get stuck here if buggy protocols don't correctly * call dev_put. */ +#define MIN_MSLEEP ((unsigned int)16) +#define MAX_MSLEEP ((unsigned int)250) static void netdev_wait_allrefs(struct net_device *dev) { unsigned long rebroadcast_time, warning_time; + unsigned int wait = MIN_MSLEEP; int refcnt; linkwatch_forget_dev(dev); @@ -10023,7 +10026,8 @@ static void netdev_wait_allrefs(struct net_device *dev) rebroadcast_time = jiffies; } - msleep(250); + msleep(wait); + wait = min(wait << 1, MAX_MSLEEP); refcnt = netdev_refcnt_read(dev);