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=-6.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 E64AAC4320A for ; Thu, 5 Aug 2021 15:33:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 962E861155 for ; Thu, 5 Aug 2021 15:33:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 962E861155 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 3F26D8D0002; Thu, 5 Aug 2021 11:33:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3A1E98D0001; Thu, 5 Aug 2021 11:33:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 290BA8D0002; Thu, 5 Aug 2021 11:33:12 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0059.hostedemail.com [216.40.44.59]) by kanga.kvack.org (Postfix) with ESMTP id 0908A8D0001 for ; Thu, 5 Aug 2021 11:33:12 -0400 (EDT) Received: from smtpin39.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id A7A14180DC6F9 for ; Thu, 5 Aug 2021 15:33:11 +0000 (UTC) X-FDA: 78441420582.39.B7608EB Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf13.hostedemail.com (Postfix) with ESMTP id 4C74A1011D47 for ; Thu, 5 Aug 2021 15:33:11 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 55A9960EE8; Thu, 5 Aug 2021 15:33:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1628177590; bh=KCw/HboD352KeqrLkTM/GnuIXejBTJnkUaCOM1fsses=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ENULft1j+sRlwYRV3nUNOTZxyyKS2cLJH+rSilFUJbM8uehCsQPCsbJyqcZa7Du+d WydicoEL7ihW+8pqqklPoDcutb2fBSCtYPW0AT3PLZkPv/ig9s78y+yVXhsPQgzeZO ViX28Azl5Z3w6iqr3jSe9GJkO6WJlZlH+EyjKeVDYh9xmjGub2+yvixEMJbvRIgEJc pr8dQUhPBbp6M6u/4sRJ/KcYdkq7jPq2C+/H9YphVULRYaEXTKRrbxlZDCOsMnuRNk tOtZnfNd3FK8HTJRyUrJfnaqf6EJRtlbpdeUBzjVoqwMDSlqM6uygStNH5ZzqY4Cmv m4h8sDMzOlJdw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 274B45C098A; Thu, 5 Aug 2021 08:33:10 -0700 (PDT) Date: Thu, 5 Aug 2021 08:33:10 -0700 From: "Paul E. McKenney" To: Andi Kleen Cc: Chao Gao , Feng Tang , kernel test robot , John Stultz , Thomas Gleixner , Stephen Boyd , Jonathan Corbet , Mark Rutland , Marc Zyngier , 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: <20210805153310.GF4397@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20210526064922.GD5262@shbuild999.sh.intel.com> <20210526134911.GB4441@paulmck-ThinkPad-P17-Gen-1> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=ENULft1j; spf=pass (imf13.hostedemail.com: domain of "SRS0=aZYB=M4=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org" designates 198.145.29.99 as permitted sender) smtp.mailfrom="SRS0=aZYB=M4=paulmck-ThinkPad-P17-Gen-1.home=paulmck@kernel.org"; dmarc=pass (policy=none) header.from=kernel.org X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4C74A1011D47 X-Stat-Signature: t8cgxuo74as8ii453ih6atrjgrm7z97d X-HE-Tag: 1628177591-711967 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 04, 2021 at 09:34:13PM -0700, Andi Kleen wrote: > > > My current thought is that if more than (say) 100 consecutive attempts > > to read the clocksource get hit with excessive delays, it is time to at > > least do a WARN_ON(), and maybe also time to disable the clocksource > > due to skew. The reason is that if reading the clocksource -always- > > sees excessive delays, perhaps the clock driver or hardware is to blame. > > > > Thoughts? > > On TDX this would be fatal because we don't have a usable fallback source > > (just jiffies). Better try as hard as possible. At some point, won't the system's suffering in silence become quite the disservice to its users? One alternative would be to give a warning splat, but avoid reporting skew. Unless there is the traditional 62.5ms of skew, of course. Thanx, Paul