From nobody Mon Feb 9 12:13:54 2026 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 9E036C53210 for ; Thu, 5 Jan 2023 01:07:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230127AbjAEBHX (ORCPT ); Wed, 4 Jan 2023 20:07:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230029AbjAEBHH (ORCPT ); Wed, 4 Jan 2023 20:07:07 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B640C30563 for ; Wed, 4 Jan 2023 17:07:05 -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 5E548B81984 for ; Thu, 5 Jan 2023 01:07:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 027F7C433F1; Thu, 5 Jan 2023 01:07:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1672880823; bh=yfdddVAsVm0wKfhUXEcuvIc8bj3pYmqk8I+8WWgBY/w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dpm8So2JL3X9PMhoZWVSdv/dq+i0y0lDDjxvZNzRpeCudBE03jip4QbBJGQxMHeSw pv/k+fHdtkYX+fYjpzTNThW48lBT5ckHs88usJbEF0VwgXRbMPs/F4Zg1jt7u4yZGW mIOjb0uHBU00ZaMyp0O887Ahv97F9p++x/6vM4EK0afW5hvRUubYuVoxhFN8efGeIo ucpSdcvf9jdsYe1lFNjh7BYHsw4CeHsBODFyNsHCk0QhB036Clj72vZZicDG44I+kB ks2Q75ka9F7YVDqMfOVEN1yJuL0rnOfl3k1tLjHEOgwb+KK2TI9c7Ae1TCfL1NNLh5 87KrokWCUWMrg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id AA98E5C086D; Wed, 4 Jan 2023 17:07:02 -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" Subject: [PATCH clocksource 2/6] clocksource: Loosen clocksource watchdog constraints Date: Wed, 4 Jan 2023 17:06:57 -0800 Message-Id: <20230105010701.1773895-2-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20230105010429.GA1773522@paulmck-ThinkPad-P17-Gen-1> References: <20230105010429.GA1773522@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, MAX_SKEW_USEC is set to 100 microseconds, which has worked reasonably well. However, NTP is willing to tolerate 500 microseconds of skew per second, and a clocksource that is good enough for NTP should be good enough for the clocksource watchdog. The watchdog's skew is controlled by MAX_SKEW_USEC and the CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option. However, these values are doubled before being associated with a clocksource's ->uncertainty_margin, and the ->uncertainty_margin values of the pair of clocksource's being compared are summed before checking against the skew. Therefore, set both MAX_SKEW_USEC and the default for the CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option to 125 microseconds of skew per second, resulting in 500 microseconds of skew per second in the clocksource watchdog's skew comparison. Suggested-by Rik van Riel Signed-off-by: Paul E. McKenney Suggested-by Rik van Riel --- kernel/time/Kconfig | 6 +++++- kernel/time/clocksource.c | 15 +++++++++------ 2 files changed, 14 insertions(+), 7 deletions(-) diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index a41753be1a2bf..bae8f11070bef 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -200,10 +200,14 @@ config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US int "Clocksource watchdog maximum allowable skew (in =CE=BCs)" depends on CLOCKSOURCE_WATCHDOG range 50 1000 - default 100 + default 125 help Specify the maximum amount of allowable watchdog skew in microseconds before reporting the clocksource to be unstable. + The default is based on a half-second clocksource watchdog + interval and NTP's maximum frequency drift of 500 parts + per million. If the clocksource is good enough for NTP, + it is good enough for the clocksource watchdog! =20 endmenu endif diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 4a2c3bb92e2e9..a3d19f6660ac7 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -95,6 +95,11 @@ static char override_name[CS_NAME_LEN]; static int finished_booting; static u64 suspend_start; =20 +/* + * Interval: 0.5sec. + */ +#define WATCHDOG_INTERVAL (HZ >> 1) + /* * Threshold: 0.0312s, when doubled: 0.0625s. * Also a default for cs->uncertainty_margin when registering clocks. @@ -106,11 +111,14 @@ static u64 suspend_start; * clocksource surrounding a read of the clocksource being validated. * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as * a lower bound for cs->uncertainty_margin values when registering clocks. + * + * The default of 500 parts per million is based on NTP's limits. + * If a clocksource is good enough for NTP, it is good enough for us! */ #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US #else -#define MAX_SKEW_USEC 100 +#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ) #endif =20 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC) @@ -140,11 +148,6 @@ static inline void clocksource_watchdog_unlock(unsigne= d long *flags) static int clocksource_watchdog_kthread(void *data); static void __clocksource_change_rating(struct clocksource *cs, int rating= ); =20 -/* - * Interval: 0.5sec. - */ -#define WATCHDOG_INTERVAL (HZ >> 1) - static void clocksource_watchdog_work(struct work_struct *work) { /* --=20 2.31.1.189.g2e36527f23