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 EB26DC433B4 for ; Mon, 26 Apr 2021 04:12:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACEC6611CC for ; Mon, 26 Apr 2021 04:12:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231431AbhDZENT (ORCPT ); Mon, 26 Apr 2021 00:13:19 -0400 Received: from mga11.intel.com ([192.55.52.93]:29774 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbhDZENS (ORCPT ); Mon, 26 Apr 2021 00:13:18 -0400 IronPort-SDR: U7R76eiWsR0VPsvaYF4T1iG7XOLBc8k24Bu3/CKsJKR6qsma+cZqu+MOXFLf17egUgaoXgKT15 zvbqcfMsTF5Q== X-IronPort-AV: E=McAfee;i="6200,9189,9965"; a="193091258" X-IronPort-AV: E=Sophos;i="5.82,251,1613462400"; d="scan'208";a="193091258" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Apr 2021 21:12:37 -0700 IronPort-SDR: poc0boSHS8hNFEnmuaRhbOJsfcCUlbhbuMNMfaMbfNts51iNwtUpXZgbS0CNYbqqnARSLPidXx sG+lRRzDQzxA== X-IronPort-AV: E=Sophos;i="5.82,251,1613462400"; d="scan'208";a="422450585" Received: from tassilo.jf.intel.com ([10.54.74.11]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Apr 2021 21:12:36 -0700 Date: Sun, 25 Apr 2021 21:12:35 -0700 From: Andi Kleen To: "Paul E. McKenney" Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org, feng.tang@intel.com, zhengjun.xing@intel.com, Chris Mason Subject: Re: [PATCH v10 clocksource 3/7] clocksource: Check per-CPU clock synchronization when marked unstable Message-ID: <20210426041235.GT1401198@tassilo.jf.intel.com> References: <20210425224540.GA1312438@paulmck-ThinkPad-P17-Gen-1> <20210425224709.1312655-3-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210425224709.1312655-3-paulmck@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 25, 2021 at 03:47:04PM -0700, Paul E. McKenney wrote: > Some sorts of per-CPU clock sources have a history of going out of > synchronization with each other. However, this problem has purportedy > been solved in the past ten years. Except that it is all too possible > that the problem has instead simply been made less likely, which might > mean that some of the occasional "Marking clocksource 'tsc' as unstable" > messages might be due to desynchronization. How would anyone know? > > Therefore apply CPU-to-CPU synchronization checking to newly unstable > clocksource that are marked with the new CLOCK_SOURCE_VERIFY_PERCPU flag. > Lists of desynchronized CPUs are printed, with the caveat that if it > is the reporting CPU that is itself desynchronized, it will appear that > all the other clocks are wrong. Just like in real life. Well I could see this causing a gigantic flood of messages then. Assume I have 300 cores, do I get all those messages 300 times repeated then? If the console is slow this might end up taking a lot of CPU time. And in a larger cluster this might not be uncommon. There must be some way to throttle this. -Andi