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 83630C4338F for ; Thu, 5 Aug 2021 04:34:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5DDA361040 for ; Thu, 5 Aug 2021 04:34:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234957AbhHEEeb (ORCPT ); Thu, 5 Aug 2021 00:34:31 -0400 Received: from mga12.intel.com ([192.55.52.136]:1627 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbhHEEea (ORCPT ); Thu, 5 Aug 2021 00:34:30 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10066"; a="193661041" X-IronPort-AV: E=Sophos;i="5.84,296,1620716400"; d="scan'208";a="193661041" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga106.fm.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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > 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 > >