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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 0852BC433B4 for ; Mon, 26 Apr 2021 15:12:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C51F761359 for ; Mon, 26 Apr 2021 15:12:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233875AbhDZPNi (ORCPT ); Mon, 26 Apr 2021 11:13:38 -0400 Received: from mga04.intel.com ([192.55.52.120]:23119 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233573AbhDZPNg (ORCPT ); Mon, 26 Apr 2021 11:13:36 -0400 IronPort-SDR: ZdF0ptpXiQj9imCouTaggO655kEtQAHGJsVdFCY0k8/irL2vvkROzoNIaLlfO2fl6a6uA47/l4 rfKs9jUFyZLg== X-IronPort-AV: E=McAfee;i="6200,9189,9966"; a="194232622" X-IronPort-AV: E=Sophos;i="5.82,252,1613462400"; d="scan'208";a="194232622" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Apr 2021 08:12:53 -0700 IronPort-SDR: RzSdqbWmxZuStb6bncQizLVdCJ7D6PKRwokbl8COVJ56sUhWUR9Oc8T8zGWfZ0dz7gT+nihC71 14W0ewhyXyiQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,252,1613462400"; d="scan'208";a="402952253" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.147.94]) by orsmga002.jf.intel.com with ESMTP; 26 Apr 2021 08:12:50 -0700 Date: Mon, 26 Apr 2021 23:12:49 +0800 From: Feng Tang To: Thomas Gleixner Cc: "Paul E. McKenney" , Xing Zhengjun , John Stultz , Stephen Boyd , Jonathan Corbet , Mark Rutland , Marc Zyngier , Andi Kleen , Chris Mason , LKML , "lkp@lists.01.org" , lkp Subject: Re: [LKP] Re: [clocksource] 6c52b5f3cf: stress-ng.opcode.ops_per_sec -14.4% regression Message-ID: <20210426151249.GA89018@shbuild999.sh.intel.com> References: <20210422074126.GA85095@shbuild999.sh.intel.com> <20210422142454.GD975577@paulmck-ThinkPad-P17-Gen-1> <20210422165743.GA162649@paulmck-ThinkPad-P17-Gen-1> <20210423061115.GA62813@shbuild999.sh.intel.com> <20210423140254.GM975577@paulmck-ThinkPad-P17-Gen-1> <20210424122920.GB85095@shbuild999.sh.intel.com> <87pmyhte2q.ffs@nanos.tec.linutronix.de> <20210426140512.GA23119@shbuild999.sh.intel.com> <87fszdt8sk.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fszdt8sk.ffs@nanos.tec.linutronix.de> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 26, 2021 at 04:33:31PM +0200, Thomas Gleixner wrote: > On Mon, Apr 26 2021 at 22:05, Feng Tang wrote: > > On Mon, Apr 26, 2021 at 08:39:25PM +0800, Thomas Gleixner wrote: > >> On Sat, Apr 24 2021 at 20:29, Feng Tang wrote: > >> > On Fri, Apr 23, 2021 at 07:02:54AM -0700, Paul E. McKenney wrote: > >> > And I'm eager to know if there is any real case of an unreliable tsc > >> > on the 'large numbers' of x86 system which complies with our cpu feature > >> > check. And if there is, my 2/2 definitely should be dropped. > >> > >> Nothing prevents BIOS tinkerers from trying to be 'smart'. My most > >> recent encounter (3 month ago) was on a laptop where TSC drifted off on > >> CPU0 very slowly, but was caught due to the TSC_ADJUST check in idle. > > > > Thanks for sharing the info! So this laptop can still work with the > > tsc_adjust check and restore, without triggering the 'unstable' alarm. > > > > Why are those BIOSes playing the trick? Maybe some other OS has hard limit > > for SMI's maxim handling time, so they try to hide the time? > > Years ago someone admitted that it was the attempt to hide the > (substantial) time wasted in SMIs from being detectable via tracing, but > obviously that backfired because TSC got out of sync. > > Since then this has mostly vanished but for some reasons it's coming > back every now and then. Rarely, but it happens still. I see now. > >> I'm still thinking about a solution to avoid that extra timer and the > >> watchdog for these systems, but haven't found anything which I don't > >> hate with a passion yet. > > > > I see. So should I hold my two patches (tsc_adjust timer and tsc watchdog > > check lifting) for a while? > > I have them on my list anyway, but yes we want to avoid the timer > because that's what the HPC / NOHZ full people are going to complain > about anyway. Got it. Thanks for the clarification! - Feng > Thanks, > > tglx