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=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 D2D4CC433B4 for ; Fri, 2 Apr 2021 20:29:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8AEFF61152 for ; Fri, 2 Apr 2021 20:29:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236041AbhDBU3b (ORCPT ); Fri, 2 Apr 2021 16:29:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:49282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229647AbhDBU3a (ORCPT ); Fri, 2 Apr 2021 16:29:30 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 54EB8610A0; Fri, 2 Apr 2021 20:29:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1617395369; bh=4yDnOxXCAIb+Rga5ly+QMhe9etGPtwP6q1XGcLulqyQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=R9CxUiZWRPm2Sweo9J+KBvk786TrI+brRyi5wlyQ/FAHykzVqgLFBZBUa/CBLu8mV HBsQbN0LHz6nfZNHU/Errk3wETcQRFMIRFrVmWUB6XP5F6SW4RxkXxlgc1vn+GboSv uUJhlTS8RjviaPZ/3NHIGIp+kZ1uVL0wg0WCxznJvdP3h/0MAClbVYxRi96XqSKxHi Mjbtmz8nsdub3aBCYSKLV38CVfBWL294naruS0fJogxqeptHOaW0KbLiJDaopDLX8e paJvJ87A8TLvP41zIxxThJ/hjyQcvHv8UeqXqmgdL7eqbnvFNUxZ5mEHda+DnpFml3 a/OZa32yW7u8Q== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 1D8BC35212A5; Fri, 2 Apr 2021 13:29:29 -0700 (PDT) Date: Fri, 2 Apr 2021 13:29:29 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: john.stultz@linaro.org, tglx@linutronix.de, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org, ak@linux.intel.com Subject: Re: [PATCH v5 clocksource] Do not mark clocks unstable due to delays for v5.13 Message-ID: <20210402202929.GA22273@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210106004013.GA11179@paulmck-ThinkPad-P72> <20210112004258.GA23158@paulmck-ThinkPad-P72> <20210202170437.GA23593@paulmck-ThinkPad-P72> <20210217212814.GA14952@paulmck-ThinkPad-P72> <20210304004931.GA25461@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210304004931.GA25461@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! If there is a sufficient delay between reading the watchdog clock and the clock under test, the clock under test will be marked unstable through no fault of its own. This series checks for this, doing limited retries to get a good set of clock reads. If the clock is marked unstable and is marked as being per-CPU, cross-CPU synchronization is checked. This series also provides delay injection, which may be enabled via kernel boot parameters to test the checking for delays. Note that "sufficient delay" can be provided by SMIs, NMIs, and of course vCPU preemption. 1. Provide module parameters to inject delays in watchdog. 2. Retry clock read if long delays detected. 3. Check per-CPU clock synchronization when marked unstable. 4. Provide a module parameter to fuzz per-CPU clock checking. 5. Do pairwise clock-desynchronization checking. Changes since v5: o Rebased to v5.12-rc5. Changes since v4: o Rebased to v5.12-rc1. Changes since v3: o Rebased to v5.11. o Apply Randy Dunlap feedback. Changes since v2: o Rebased to v5.11-rc6. o Updated Cc: list. Changes since v1: o Applied feedback from Rik van Riel. o Rebased to v5.11-rc3. o Stripped "RFC" from the subject lines. Thanx, Paul ------------------------------------------------------------------------ Documentation/admin-guide/kernel-parameters.txt | 38 +++++ arch/x86/kernel/kvmclock.c | 2 arch/x86/kernel/tsc.c | 3 include/linux/clocksource.h | 2 kernel/time/clocksource.c | 174 +++++++++++++++++++++--- 5 files changed, 195 insertions(+), 24 deletions(-)