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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 4747EC43214 for ; Thu, 5 Aug 2021 11:51:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F774610A8 for ; Thu, 5 Aug 2021 11:51:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241142AbhHELwK (ORCPT ); Thu, 5 Aug 2021 07:52:10 -0400 Received: from foss.arm.com ([217.140.110.172]:43352 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241116AbhHELwJ (ORCPT ); Thu, 5 Aug 2021 07:52:09 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 317291042; Thu, 5 Aug 2021 04:51:55 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 429323F719; Thu, 5 Aug 2021 04:51:53 -0700 (PDT) From: Valentin Schneider To: paulmck@kernel.org Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-rt-users@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , Frederic Weisbecker , Josh Triplett , Davidlohr Bueso , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes Subject: Re: [PATCH 2/2] rcutorture: Nudge ksoftirqd priority for RCU boost testing In-Reply-To: <20210804225332.GB4397@paulmck-ThinkPad-P17-Gen-1> References: <20210803225437.3612591-1-valentin.schneider@arm.com> <20210803225437.3612591-3-valentin.schneider@arm.com> <20210803234231.GW4397@paulmck-ThinkPad-P17-Gen-1> <87tuk5a4yk.mognet@arm.com> <20210804225332.GB4397@paulmck-ThinkPad-P17-Gen-1> Date: Thu, 05 Aug 2021 12:51:48 +0100 Message-ID: <87mtpw9kiz.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/08/21 15:53, Paul E. McKenney wrote: > On Wed, Aug 04, 2021 at 11:18:11AM +0100, Valentin Schneider wrote: >> >> Hm so v5.13-rt1 has this commit: >> >> 5e59fba573e6 ("rcutorture: Fix testing of RCU priority boosting") >> >> which gates RCU boost torture testing under CONFIG_PREEMPT_RT. Now, AFAICT >> the TIMER_SOFTIRQ priority problem is there regardless of >> CONFIG_PREEMPT_RT, so this patch would (should?) make sense even on >> !CONFIG_PREEMPT_RT. > > What rcutorture scenario TREE03 does is to boot with tree.use_softirq=0 > and threadirqs. I see your point about timers and softirq, but this > does run reliably for me. > > Ah, I see why. Commit ea6d962e80b6 ("rcutorture: Judge RCU priority > boosting on grace periods, not callbacks") includes boosting the priority > of the ksoftirqd kthreads. But only when running rcutorture builtin, > not as a module. Here is the code in rcu_torture_init(): > > // Testing RCU priority boosting requires rcutorture do > // some serious abuse. Counter this by running ksoftirqd > // at higher priority. > if (IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) { > for_each_online_cpu(cpu) { > struct sched_param sp; > struct task_struct *t; > > t = per_cpu(ksoftirqd, cpu); > WARN_ON_ONCE(!t); > sp.sched_priority = 2; > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > } > } > > I take it that you were running rcutorture as a module? > > This describes how to run it built-in, if that works for you: > > https://paulmck.livejournal.com/61432.html > > More specifically: https://paulmck.livejournal.com/57769.html > > Alternatively, the "IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)" check could be > removed in the above code, and the ksoftirqd kthreads could have their > original priority restored in rcu_torture_cleanup(). > > Thoughts? > I actually run rcutorture as a builtin, but from what I can tell the above patch came in v5.14-rc1, and ofc I'm running my tests on v5.13-rt1... I should have paid closer attention to what was in the latest mainline, apologies for the noise. FWIW tweaking ksoftirqd priority only when the torture module is builtin makes sense to me.