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 8EB27C4332F for ; Mon, 14 Nov 2022 23:28:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236889AbiKNX2p (ORCPT ); Mon, 14 Nov 2022 18:28:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236642AbiKNX2d (ORCPT ); Mon, 14 Nov 2022 18:28:33 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 935E92A4 for ; Mon, 14 Nov 2022 15:28:31 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 4CD4AB815FC for ; Mon, 14 Nov 2022 23:28:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2D6BC433B5; Mon, 14 Nov 2022 23:28:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1668468509; bh=ZjS+OKGtE62BjR1npWFo6xbmcHIB1kAdTslp2K20OB8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=s8NlDZxiV/u067KU7C3YtF9zAQMKW5UVHP2/5BJ7oZc7OZXi1teKrv56PH4rgoqtB /Xz4IV2JIkrnzU5g7ZBl50S2PzuQxzvcmZJTOKm42B+H4fOmRkTcM+VmG7B/Lz4pQ8 5/tJVZPu/8o2rzZrFMryalyu7GfsPoCLeb1aNi9fL/sZVMpMQ31ZRPL1tV0F/LaNDA 4T8whGVExx4YhJUByU82/jCN/4R5EYdQRTNACcfmO1NonrIzHq3OkSi6tWL2AkfrZC Kt/jjSIPIilpZclEqR5fCHZGZ09PplUdCguPGAxD+oEJrURs3jRRABI8nmix3lyU9q TRzDPILoFgNLQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 91E705C16C5; Mon, 14 Nov 2022 15:28:28 -0800 (PST) From: "Paul E. McKenney" To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@meta.com, neeraju@codeaurora.org, ak@linux.intel.com, feng.tang@intel.com, zhengjun.xing@intel.com, "Paul E. McKenney" , Waiman Long , John Stultz Subject: [PATCH clocksource 2/3] clocksource: Add comments to classify bogus measurements Date: Mon, 14 Nov 2022 15:28:25 -0800 Message-Id: <20221114232827.835599-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> References: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org An extremely busy system can delay the clocksource watchdog, so that the corresponding too-long bogus-measurement error does not necessarily imply an error in the system. However, a too-short bogus-measurement error likely indicates a bug in hardware, firmware or software. Therefore, add comments clarifying these bogus-measurement pr_warn()s. Reported-by: Feng Tang Signed-off-by: Paul E. McKenney Reviewed-by: Waiman Long Reviewed-by: Feng Tang Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd --- kernel/time/clocksource.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index dcaf38c062161..3f5317faf891f 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -443,10 +443,12 @@ static void clocksource_watchdog(struct timer_list *unused) /* Check for bogus measurements. */ wdi = jiffies_to_nsecs(WATCHDOG_INTERVAL); if (wd_nsec < (wdi >> 2)) { + /* This usually indicates broken timer code or hardware. */ pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced only %lld ns during %d-jiffy time interval, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); continue; } if (wd_nsec > (wdi << 2)) { + /* This can happen on busy systems, which can delay the watchdog. */ pr_warn("timekeeping watchdog on CPU%d: Watchdog clocksource '%s' advanced an excessive %lld ns during %d-jiffy time interval, probable CPU overutilization, skipping watchdog check.\n", smp_processor_id(), watchdog->name, wd_nsec, WATCHDOG_INTERVAL); continue; } -- 2.31.1.189.g2e36527f23