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=-5.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 88A43C4338F for ; Thu, 5 Aug 2021 04:34:23 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0A43361073 for ; Thu, 5 Aug 2021 04:34:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0A43361073 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 6B2068D0001; Thu, 5 Aug 2021 00:34:22 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 661E56B0071; Thu, 5 Aug 2021 00:34:22 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5520D8D0001; Thu, 5 Aug 2021 00:34:22 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0042.hostedemail.com [216.40.44.42]) by kanga.kvack.org (Postfix) with ESMTP id 380A06B006C for ; Thu, 5 Aug 2021 00:34:22 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 5014A8249980 for ; Thu, 5 Aug 2021 04:34:20 +0000 (UTC) X-FDA: 78439760280.13.D35580C Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) by imf18.hostedemail.com (Postfix) with ESMTP id 1E70140020A5 for ; Thu, 5 Aug 2021 04:34:18 +0000 (UTC) X-IronPort-AV: E=McAfee;i="6200,9189,10066"; a="275117760" X-IronPort-AV: E=Sophos;i="5.84,296,1620716400"; d="scan'208";a="275117760" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Aug 2021 21:34:16 -0700 X-IronPort-AV: E=Sophos;i="5.84,296,1620716400"; d="scan'208";a="522296741" Received: from akleen-mobl1.amr.corp.intel.com (HELO [10.209.32.138]) ([10.209.32.138]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Aug 2021 21:34:15 -0700 Subject: Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5% regression To: paulmck@kernel.org, Chao Gao Cc: 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 References: <20210521135617.GT4441@paulmck-ThinkPad-P17-Gen-1> <20210522160827.GA2625834@paulmck-ThinkPad-P17-Gen-1> <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> From: Andi Kleen Message-ID: Date: Wed, 4 Aug 2021 21:34:13 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210805040349.GD4397@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 1E70140020A5 Authentication-Results: imf18.hostedemail.com; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=intel.com (policy=none); spf=none (imf18.hostedemail.com: domain of ak@linux.intel.com has no SPF policy when checking 134.134.136.31) smtp.mailfrom=ak@linux.intel.com X-Stat-Signature: 5oa9wabepgadwab3kfkqcd73gkuyjzys X-HE-Tag: 1628138058-337450 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: > 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. -Andi > >