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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E02DC433EF for ; Wed, 1 Dec 2021 01:27:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346138AbhLABaY (ORCPT ); Tue, 30 Nov 2021 20:30:24 -0500 Received: from mga01.intel.com ([192.55.52.88]:24840 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230476AbhLABaU (ORCPT ); Tue, 30 Nov 2021 20:30:20 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10184"; a="260326756" X-IronPort-AV: E=Sophos;i="5.87,277,1631602800"; d="scan'208";a="260326756" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Nov 2021 17:27:00 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,277,1631602800"; d="scan'208";a="500023263" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.146.189]) by orsmga007.jf.intel.com with ESMTP; 30 Nov 2021 17:26:56 -0800 Date: Wed, 1 Dec 2021 09:26:55 +0800 From: Feng Tang To: "Paul E. McKenney" Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org, rui.zhang@intel.com, andi.kleen@intel.com, len.brown@intel.com, tim.c.chen@intel.com Subject: Re: [PATCH v3 2/2] x86/tsc: skip tsc watchdog checking for qualified platforms Message-ID: <20211201012655.GA20240@shbuild999.sh.intel.com> References: <20211130064623.GB96474@shbuild999.sh.intel.com> <20211130144048.GQ641268@paulmck-ThinkPad-P17-Gen-1> <20211130150256.GA19477@shbuild999.sh.intel.com> <20211130162815.GU641268@paulmck-ThinkPad-P17-Gen-1> <87r1axbcor.ffs@tglx> <20211130204721.GZ641268@paulmck-ThinkPad-P17-Gen-1> <87ilw9b95q.ffs@tglx> <20211130224825.GA641268@paulmck-ThinkPad-P17-Gen-1> <87tuft9qpc.ffs@tglx> <20211130233726.GD641268@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211130233726.GD641268@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 30, 2021 at 03:37:26PM -0800, Paul E. McKenney wrote: > On Wed, Dec 01, 2021 at 12:19:43AM +0100, Thomas Gleixner wrote: > > On Tue, Nov 30 2021 at 14:48, Paul E. McKenney wrote: > > > On Tue, Nov 30, 2021 at 10:55:45PM +0100, Thomas Gleixner wrote: > > >> > OK, HPET or nothing, then. > > >> > > >> Older machines also have pm_timer. But those beasts seem to have lost > > >> that too. > > > > > > I suppose that one way of avoiding clock-skew messages is to have only > > > one clock. > > > > Indeed. It's a complete mystery why it takes ages to implement reliable > > clocks in hardware. > > That one is easy. It is because the previous clocksource watchdog was > too lenient. ;-) > > (Sorry, couldn't resist...) > > > >> >> We really need to remove the watchdog requirement for modern hardware. > > >> >> Let me stare at those patches and get them merged. > > >> > > > >> > You are more trusting of modern hardware than I am, but for all I know, > > >> > maybe rightfully so. ;-) > > >> > > >> Well, I rather put a bet on the hardware, which has become reasonable > > >> over the last decade, than on trying to solve a circular dependency > > >> problem with tons of heuristics which won't ever work correctly. > > > > > > Use of HPET to check the interval length would not be circular, right? > > > > As long as the HPET works reliably :) > > Is it also a complete mystery why clocksources previously deemed > reliable no longer work reliably? ;-) For HPET, it's a long story :) Back in 2012 or so, the HPET on Baytrail platform has a new feature that it will stop counting in PC10 (a cpuidle state), which prevent it to be a clocksource, and we have to disable HPET explicitly for that platform. Since then, some new platforms also have the same feature, and their HPET got disabled too. Thanks, Feng