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=-6.2 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 3D0D1C433B4 for ; Mon, 26 Apr 2021 15:28:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 05ACA6135A for ; Mon, 26 Apr 2021 15:28:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234029AbhDZP2p (ORCPT ); Mon, 26 Apr 2021 11:28:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:34412 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233674AbhDZP2n (ORCPT ); Mon, 26 Apr 2021 11:28:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2C6EB61076; Mon, 26 Apr 2021 15:28:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1619450882; bh=AwhTbcawstyLCkCKuD8TwEtnhQvod3F3gZm+IW/Bb6I=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=dRmOo9ZVfxCtmfBY5Durmki5k7x6WWssiMaFS3cJxfhed9VJTllzhWaHAb5tArLjT x/Vk2e1SXMq734AzV8ResxZtLdhvYHSvEqXcm7Mevh3lsx7pOEV6aNFWjidjF9SZ3w yskZeVInlhAS2UbE1gcnSNHwRW+CsaEcoz2OFxT1dY4KlgYc4n6dw/jqltMGPsXNJN VFX4UNzPOlrNxBPZLQYTmQWopzS1H3KWlY7lK9DTs/BsK5aQY49DvUulM7SPqHxV8q pVal0imAxPwzOXKS3aSNln4VeOlEPi9Bgf0ta60E5acV6zpnuxlmE2zU9Uyj8K4F44 PcibNCL8XYtRw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id D36E85C0121; Mon, 26 Apr 2021 08:28:01 -0700 (PDT) Date: Mon, 26 Apr 2021 08:28:01 -0700 From: "Paul E. McKenney" To: Andi Kleen Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org, feng.tang@intel.com, zhengjun.xing@intel.com, Chris Mason Subject: Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog Message-ID: <20210426152801.GY975577@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20210425224540.GA1312438@paulmck-ThinkPad-P17-Gen-1> <20210425224709.1312655-1-paulmck@kernel.org> <20210426040736.GS1401198@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210426040736.GS1401198@tassilo.jf.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 25, 2021 at 09:07:36PM -0700, Andi Kleen wrote: [ . . . ] > > + clocksource.inject_delay_period= [KNL] > > + Number of calls to clocksource_watchdog() before > > + delays are injected between reads from the > > + two clocksources. Values of zero disable this > > + delay injection. These delays can cause clocks > > + to be marked unstable, so use of this parameter > > + should therefore be avoided on production systems. > > + Defaults to zero (disabled). > > + > > + clocksource.inject_delay_repeat= [KNL] > > + Number of repeated clocksource_watchdog() delay > > + injections per period. If inject_delay_period > > + is five and inject_delay_repeat is three, there > > + will be five delay-free reads followed by three > > + delayed reads. > > I'm not sure command line options are the right way to do this. > How about integrating it with the fault injection framework in debugfs. > > This way syzkaller etc. can play with it, which long term would > give much better test coverage. > > This wouldn't allow boot time coverage, but presumably that's not > too important here. Boot-time coverage is important, as we saw in kbuild test robot testing of v9 of this patchset, which triggered clocksource_tsc_early, but not clocksource_tsc. Note that v10 avoids this triggering. Thanx, Paul