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=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 5D0C6C54F45 for ; Fri, 4 Sep 2020 18:10:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9EB521D42 for ; Fri, 4 Sep 2020 18:01:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728306AbgIDRkw (ORCPT ); Fri, 4 Sep 2020 13:40:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:38416 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728255AbgIDRkX (ORCPT ); Fri, 4 Sep 2020 13:40:23 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AA18CB6C2; Fri, 4 Sep 2020 17:40:22 +0000 (UTC) Date: Fri, 4 Sep 2020 10:24:32 -0700 From: Davidlohr Bueso To: "Paul E. McKenney" Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, linux-kernel@vger.kernel.org Subject: Re: Question on task_blocks_on_rt_mutex() Message-ID: <20200904172432.wgxn6x5tpnt4lcln@linux-p48b> References: <20200831224911.GA13114@paulmck-ThinkPad-P72> <20200831232130.GA28456@paulmck-ThinkPad-P72> <20200901174938.GA8158@paulmck-ThinkPad-P72> <20200901235821.GA8516@paulmck-ThinkPad-P72> <20200902015128.wsulcxhbo7dutcjz@linux-p48b> <20200902155410.GH29330@paulmck-ThinkPad-P72> <20200903200639.GA8956@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200903200639.GA8956@paulmck-ThinkPad-P72> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 03 Sep 2020, Paul E. McKenney wrote: >commit d93a64389f4d544ded241d0ba30b2586497f5dc0 >Author: Paul E. McKenney >Date: Tue Sep 1 16:58:41 2020 -0700 > > torture: Periodically pause in stutter_wait() > > Running locktorture scenario LOCK05 results in hangs: > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --torture lock --duration 3 --configs LOCK05 > > The lock_torture_writer() kthreads set themselves to MAX_NICE while > running SCHED_OTHER. Other locktorture kthreads run at default niceness, > also SCHED_OTHER. This results in these other locktorture kthreads > indefinitely preempting the lock_torture_writer() kthreads. Note that > the cond_resched() in the stutter_wait() function's loop is ineffective > because this scenario is built with CONFIG_PREEMPT=y. > > It is not clear that such indefinite preemption is supposed to happen, but > in the meantime this commit prevents kthreads running in stutter_wait() > from being completely CPU-bound, thus allowing the other threads to get > some CPU in a timely fashion. This commit also uses hrtimers to provide > very short sleeps to avoid degrading the sudden-on testing that stutter > is supposed to provide. > > Signed-off-by: Paul E. McKenney Reviwed-by: Davidlohr Bueso