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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5588EDE9A5 for ; Thu, 14 Sep 2023 11:11:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232633AbjINLLh (ORCPT ); Thu, 14 Sep 2023 07:11:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233919AbjINLLf (ORCPT ); Thu, 14 Sep 2023 07:11:35 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A6DA11FD4 for ; Thu, 14 Sep 2023 04:11:30 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 157DCC433CA; Thu, 14 Sep 2023 11:11:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1694689890; bh=Py3gKDehUdo/afmDk2Anr7QNPtfiRxlC229LID+1dPY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=sucrBlkZdN8egzWdxSHw4wIjeL0PZGNAizGH2Jmw9TJyRz7rGbdoACvjrPe3olFNw Ll26LDN4SluMld6j9pzyu05teIN6UaeaV/iX64Xzwj+GvS8i3rVx5TvTiihFIUYts5 KY/IbT+KQWAl8DR0tdqUxbaEm/EwzJWwhn8fL0mQWu34mUdl3ygGetOFiynetcFpBZ MUpM/23QQLwe2FcYdZ0UYwo//grEAHO7YktrqBLK+fDQ78if/OwYOlK96C7hu5CJft SfX269tDaIw3OSw67qcTtFRiAAV+47YHI3/+MixQGFnUUPd2CZvu5SabjByOG6Dg7q 6zXDN9oR9XN8w== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 3BB3CCE0D10; Thu, 14 Sep 2023 04:11:26 -0700 (PDT) Date: Thu, 14 Sep 2023 04:11:26 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: Frederic Weisbecker , rcu@vger.kernel.org Subject: Re: [BUG] Random intermittent boost failures (Was Re: [BUG] TREE04..) Message-ID: Reply-To: paulmck@kernel.org References: <20230910201445.GA1605059@google.com> <20230911022725.GA2542634@google.com> <1f12ffe6-4cb0-4364-8c4c-3393ca5368c2@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Wed, Sep 13, 2023 at 04:30:20PM -0400, Joel Fernandes wrote: > On Mon, Sep 11, 2023 at 4:16 AM Paul E. McKenney wrote: > [..] > > > I am digging deeper to see why the rcu_preempt thread cannot be pushed out > > > and then I'll also look at why is it being pushed out in the first place. > > > > > > At least I have a strong repro now running 5 instances of TREE03 in parallel > > > for several hours. > > > > Very good! Then why not boot with rcutorture.onoff_interval=0 and see if > > the problem still occurs? If yes, then there is definitely some reason > > other than CPU hotplug that makes this happen. > > Hi Paul, > So looks so far like onoff_interval=0 makes the issue disappear. So > likely hotplug related. I am ok with doing the cpus_read_lock during > boost testing and seeing if that fixes it. If it does, I can move on > to the next thing in my backlog. > > What do you think? Or should I spend more time root-causing it? It is > most like runaway RT threads combined with the CPU hotplug threads, > making scheduling of the rcu_preempt thread not happen. But I can't > say for sure without more/better tracing (Speaking of better tracing, > I am adding core-dump support to rcutorture, but it is not there yet). This would not be the first time rcutorture has had trouble with those threads, so I am for adding the cpus_read_lock(). Additional root-causing might be helpful, but then again, you might have higher priority things to worry about. ;-) Thanx, Paul