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=-11.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BEEF1C432BE for ; Fri, 6 Aug 2021 04:15:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A4340611CC for ; Fri, 6 Aug 2021 04:15:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242280AbhHFEPU (ORCPT ); Fri, 6 Aug 2021 00:15:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:59956 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229836AbhHFEPS (ORCPT ); Fri, 6 Aug 2021 00:15:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5DD9860EBC; Fri, 6 Aug 2021 04:15:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1628223303; bh=iOjc/0/HUU3pEtEtet4Pzyq7t3h6ygOVDXTBFLZaatg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=hvzWNnPqmGH4WsnZwgRgRIkOvZyglo8QxliWthkiCx+bdBcFZDgMFPebLtOGOdcUn sh6hZbTT8E2TaLPqByA9yx2KTleUDf7pBdsamhqMU+Cgq/Pc5FvFXy2nvEbjEuoiDE msWOxH1A6b9Cv/sbhMB/P11HW6E8Ve1DKaczfXdk1yzaZC7u8z6GijYQuqPqcUR6b5 +ULCULAC6vCuXeJFQQjk0DMrGStaksRv8yfzXV8CM66qxEpOWKGL8anFVaPtg3CvUU SAFGpEPCk9XfYAXbCHy2+bcALpeQ1XDXRrbRWDDOfPYtV3MLK47iB5JMSOgK97/Ti/ 6yZlRRYao97Jg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 2239A5C1722; Thu, 5 Aug 2021 21:15:03 -0700 (PDT) Date: Thu, 5 Aug 2021 21:15:03 -0700 From: "Paul E. McKenney" To: Chao Gao Cc: Feng Tang , kernel test robot , John Stultz , Thomas Gleixner , Stephen Boyd , Jonathan Corbet , Mark Rutland , Marc Zyngier , Andi Kleen , Xing Zhengjun , Chris Mason , LKML , Linux Memory Management List , lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com, zhengjun.xing@intel.com Subject: Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5% regression Message-ID: <20210806041503.GO4397@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20210527182959.GA437082@paulmck-ThinkPad-P17-Gen-1> <20210802062008.GA24720@gao-cwp> <20210802170257.GL4397@paulmck-ThinkPad-P17-Gen-1> <20210803085759.GA31621@gao-cwp> <20210803134816.GO4397@paulmck-ThinkPad-P17-Gen-1> <20210805021646.GA11629@gao-cwp> <20210805040349.GD4397@paulmck-ThinkPad-P17-Gen-1> <20210805053938.GA12593@gao-cwp> <20210805153727.GG4397@paulmck-ThinkPad-P17-Gen-1> <20210806020958.GA18104@gao-cwp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210806020958.GA18104@gao-cwp> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 06, 2021 at 10:10:00AM +0800, Chao Gao wrote: > On Thu, Aug 05, 2021 at 08:37:27AM -0700, Paul E. McKenney wrote: > >On Thu, Aug 05, 2021 at 01:39:40PM +0800, Chao Gao wrote: > >> [snip] > >> >> This patch works well; no false-positive (marking TSC unstable) in a > >> >> 10hr stress test. > >> > > >> >Very good, thank you! May I add your Tested-by? > >> > >> sure. > >> Tested-by: Chao Gao > > > >Very good, thank you! I will apply this on the next rebase. > > > >> >I expect that I will need to modify the patch a bit more to check for > >> >a system where it is -never- able to get a good fine-grained read from > >> >the clock. > >> > >> Agreed. > >> > >> >And it might be that your test run ended up in that state. > >> > >> Not that case judging from kernel logs. Coarse-grained check happened 6475 > >> times in 43k seconds (by grep "coarse-grained skew check" in kernel logs). > >> So, still many checks were fine-grained. > > > >Whew! ;-) > > > >So about once per 13 clocksource watchdog checks. > > > >To Andi's point, do you have enough information in your console log to > >work out the longest run of course-grained clocksource checks? > > Yes. 5 consecutive course-grained clocksource checks. Note that > considering the reinitialization after course-grained check, in my > calculation, two course-grained checks are considered consecutive if > they happens in 1s(+/- 0.3s). Very good, thank you! So it seems eminently reasonable to have the clocksource watchdog complain bitterly for more than (say) 100 consecutive course-grained checks. I am thinking in terms of a separate patch for this purpose. Thoughts? Thanx, Paul