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 96634C4338F for ; Thu, 5 Aug 2021 15:33:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7BBD260F35 for ; Thu, 5 Aug 2021 15:33:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238390AbhHEPdZ (ORCPT ); Thu, 5 Aug 2021 11:33:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:42794 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230298AbhHEPdY (ORCPT ); Thu, 5 Aug 2021 11:33:24 -0400 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: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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