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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 12DF3C47259 for ; Tue, 5 May 2020 18:49:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6711206FA for ; Tue, 5 May 2020 18:49:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588704598; bh=KfOJ1bNlaBRu8hNC+oQtr3+NZ5WeNHLWOHTP2GwjliM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=wwlqg06ro1QA0vzn6FpukdWYQ2gLl+fKVUrqJ64jGN7em2aE5FHMDyuzEx5IVzMaM CSF0d03HcjnwZrUaBjZoMXA7WNpQTeRw1dP5XyJal9IY1oP/cDz8Zdz/2rdGYXtDvD 6k0Oe3cWtCFxPNoFZBAmF3mlh4rdqS0gZpMMQdcU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729001AbgEESt4 (ORCPT ); Tue, 5 May 2020 14:49:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:49416 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728807AbgEESt4 (ORCPT ); Tue, 5 May 2020 14:49:56 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 834BC206CC; Tue, 5 May 2020 18:49:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588704595; bh=KfOJ1bNlaBRu8hNC+oQtr3+NZ5WeNHLWOHTP2GwjliM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=N26Rhli2ECY6OsVWpu0QZfXZx6Hiyng83I0UMdIeKFPVXyYSAZd9O8K8X3uN6LANm QSk++JhskOjRmP/vlrsFMH61hn0NUyv5yN70YuZb+M9GsdEaAtYFUmNLj34XSphAMB NbkcIu0eE1+w5NEe+jPRrqmGde9LfNd8FNnLy/5E= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 64AAB3523039; Tue, 5 May 2020 11:49:55 -0700 (PDT) Date: Tue, 5 May 2020 11:49:55 -0700 From: "Paul E. McKenney" To: SeongJae Park Cc: Eric Dumazet , Eric Dumazet , David Miller , Al Viro , Jakub Kicinski , Greg Kroah-Hartman , sj38.park@gmail.com, netdev , LKML , SeongJae Park , snu@amazon.com, amit@kernel.org, stable@vger.kernel.org Subject: Re: Re: Re: Re: [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change Message-ID: <20200505184955.GO2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200505181707.GJ2869@paulmck-ThinkPad-P72> <20200505183402.2021-1-sjpark@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200505183402.2021-1-sjpark@amazon.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, May 05, 2020 at 08:34:02PM +0200, SeongJae Park wrote: > On Tue, 5 May 2020 11:17:07 -0700 "Paul E. McKenney" wrote: > > > On Tue, May 05, 2020 at 07:56:05PM +0200, SeongJae Park wrote: > > > On Tue, 5 May 2020 10:30:36 -0700 "Paul E. McKenney" wrote: > > > > > > > On Tue, May 05, 2020 at 07:05:53PM +0200, SeongJae Park wrote: > > > > > On Tue, 5 May 2020 09:37:42 -0700 Eric Dumazet wrote: > > > > > > > > > > > > > > > > > > > > > > > On 5/5/20 9:31 AM, Eric Dumazet wrote: > > > > > > > > > > > > > > > > > > > > > On 5/5/20 9:25 AM, Eric Dumazet wrote: > > > > > > >> > > > > > > >> > > > > > > >> On 5/5/20 9:13 AM, SeongJae Park wrote: > > > > > > >>> On Tue, 5 May 2020 09:00:44 -0700 Eric Dumazet wrote: > > > > > > >>> > > > > > > >>>> On Tue, May 5, 2020 at 8:47 AM SeongJae Park wrote: > > > > > > >>>>> > > > > > > >>>>> On Tue, 5 May 2020 08:20:50 -0700 Eric Dumazet wrote: > > > > > > >>>>> > > > > > > >>>>>> > > > > > > >>>>>> > > > > > > >>>>>> On 5/5/20 8:07 AM, SeongJae Park wrote: > > > > > > >>>>>>> On Tue, 5 May 2020 07:53:39 -0700 Eric Dumazet wrote: > > > > > > >>>>>>> > > > > > > >>>>>> > > > > > [...] > > > > > > >> > > > > > > >> I would ask Paul opinion on this issue, because we have many objects > > > > > > >> being freed after RCU grace periods. > > > > > > >> > > > > > > >> If RCU subsystem can not keep-up, I guess other workloads will also suffer. > > > > > > >> > > > > > > >> Sure, we can revert patches there and there trying to work around the issue, > > > > > > >> but for objects allocated from process context, we should not have these problems. > > > > > > >> > > > > > > > > > > > > > > I wonder if simply adjusting rcu_divisor to 6 or 5 would help > > > > > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > > > index d9a49cd6065a20936edbda1b334136ab597cde52..fde833bac0f9f81e8536211b4dad6e7575c1219a 100644 > > > > > > > --- a/kernel/rcu/tree.c > > > > > > > +++ b/kernel/rcu/tree.c > > > > > > > @@ -427,7 +427,7 @@ module_param(qovld, long, 0444); > > > > > > > static ulong jiffies_till_first_fqs = ULONG_MAX; > > > > > > > static ulong jiffies_till_next_fqs = ULONG_MAX; > > > > > > > static bool rcu_kick_kthreads; > > > > > > > -static int rcu_divisor = 7; > > > > > > > +static int rcu_divisor = 6; > > > > > > > module_param(rcu_divisor, int, 0644); > > > > > > > > > > > > > > /* Force an exit from rcu_do_batch() after 3 milliseconds. */ > > > > > > > > > > > > > > > > > > > To be clear, you can adjust the value without building a new kernel. > > > > > > > > > > > > echo 6 >/sys/module/rcutree/parameters/rcu_divisor > > > > > > > > > > I tried value 6, 5, and 4, but none of those removed the problem. > > > > > > > > Thank you for checking this! > > > > > > > > Was your earlier discussion on long RCU readers speculation, or do you > > > > have measurements? > > > > > > It was just a guess without any measurement or dedicated investigation. > > > > OK, another thing to check is the duration of the low-memory episode. > > Does this duration exceed the RCU CPU stall warning time? (21 seconds > > in mainline, 60 in many distros, but check rcupdate.rcu_cpu_stall_timeout > > to be sure.) > > The benchmark takes about 36 seconds for 10,000 repeats of the test. > > The value on the test machine is 60. > > So the duration would not exceeded the warning time and therefore I haven't > seen the warning message. > > As told in other mail, I will also adjust this value to shorter one. Sounds good, thank you! > > Also, any chance of a .config? Or at least the RCU portions? I am > > guessing CONFIG_PREEMPT=n, for example. > > I guess this would be ok. > > # CONFIG_PREEMPT is not set > > # > # RCU Subsystem > # > CONFIG_TREE_RCU=y > CONFIG_RCU_EXPERT=y > CONFIG_SRCU=y > CONFIG_TREE_SRCU=y > CONFIG_RCU_STALL_COMMON=y > CONFIG_RCU_NEED_SEGCBLIST=y > CONFIG_RCU_FANOUT=64 > CONFIG_RCU_FANOUT_LEAF=16 > # CONFIG_RCU_FAST_NO_HZ is not set > CONFIG_RCU_NOCB_CPU=y > # end of RCU Subsystem And thank you again! Thanx, Paul