From nobody Fri Sep 12 04:39:42 2025 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 17D50C636D4 for ; Mon, 13 Feb 2023 18:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229968AbjBMSsx (ORCPT ); Mon, 13 Feb 2023 13:48:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42366 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229785AbjBMSsg (ORCPT ); Mon, 13 Feb 2023 13:48:36 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 87E861CAF7; Mon, 13 Feb 2023 10:48:34 -0800 (PST) Date: Mon, 13 Feb 2023 18:48:32 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1676314113; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=dHNwsm3yjCynJiuBVDd4PecaPqNLpHOjRsyZeHKr3qY=; b=pmO8TXtcqUB4dMLm7Sydu/bUb+k99sw4nS6k3ZFSGA6qUWaegXw2S6fIHKA/ER37MKBkHb SzcpguwcdjqK9uZ46lzMSHk6RX/t7HNdq3lymr8LJBLlpxCEnhD2rHS6hkLO8Ci6GWr6mH gS0qGzCs0kAiFMIPOoKWCNsfV4Q7jaH/lEk/z1ENhHyFzumD37Vw2K/jkIDJF+9azBQJ4f vhxfJV5PJyWNEdHCIk0XGyX66xxFUkWlcgJXKC1j7RTJwhrlg0w2kbQcAhSMtSXEChj3+A 7tWIhMFp28x4CYbuOCtx3Axucf5UB7b6gfup1zcyZ8RqF4ijUVuVC+FeNhuXUg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1676314113; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=dHNwsm3yjCynJiuBVDd4PecaPqNLpHOjRsyZeHKr3qY=; b=4AZpTZsTzJkzLnqTbYHBIOZ9ylCcYLficUw7uwbh0t9UZE8NesAy+xa+nk1qoKGWs1lSBb Hx83R7GDqKYEt0Bg== From: "tip-bot2 for Feng Tang" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] clocksource: Suspend the watchdog temporarily when high read latency detected Cc: Feng Tang , Waiman Long , John Stultz , Thomas Gleixner , Stephen Boyd , "Paul E. McKenney" , x86@kernel.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-ID: <167631411278.4906.130996180925938138.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the timers/core branch of tip: Commit-ID: b7082cdfc464bf9231300605d03eebf943dda307 Gitweb: https://git.kernel.org/tip/b7082cdfc464bf9231300605d03eebf94= 3dda307 Author: Feng Tang AuthorDate: Tue, 20 Dec 2022 16:25:12 +08:00 Committer: Paul E. McKenney CommitterDate: Tue, 24 Jan 2023 15:12:48 -08:00 clocksource: Suspend the watchdog temporarily when high read latency detect= ed Bugs have been reported on 8 sockets x86 machines in which the TSC was wrongly disabled when the system is under heavy workload. [ 818.380354] clocksource: timekeeping watchdog on CPU336: hpet wd-wd read= -back delay of 1203520ns [ 818.436160] clocksource: wd-tsc-wd read-back delay of 181880ns, clock-sk= ew test skipped! [ 819.402962] clocksource: timekeeping watchdog on CPU338: hpet wd-wd read= -back delay of 324000ns [ 819.448036] clocksource: wd-tsc-wd read-back delay of 337240ns, clock-sk= ew test skipped! [ 819.880863] clocksource: timekeeping watchdog on CPU339: hpet read-back = delay of 150280ns, attempt 3, marking unstable [ 819.936243] tsc: Marking TSC unstable due to clocksource watchdog [ 820.068173] TSC found unstable after boot, most likely due to broken BIO= S. Use 'tsc=3Dunstable'. [ 820.092382] sched_clock: Marking unstable (818769414384, 1195404998) [ 820.643627] clocksource: Checking clocksource tsc synchronization from C= PU 267 to CPUs 0,4,25,70,126,430,557,564. [ 821.067990] clocksource: Switched to clocksource hpet This can be reproduced by running memory intensive 'stream' tests, or some of the stress-ng subcases such as 'ioport'. The reason for these issues is the when system is under heavy load, the read latency of the clocksources can be very high. Even lightweight TSC reads can show high latencies, and latencies are much worse for external clocksources such as HPET or the APIC PM timer. These latencies can result in false-positive clocksource-unstable determinations. These issues were initially reported by a customer running on a production system, and this problem was reproduced on several generations of Xeon servers, especially when running the stress-ng test. These Xeon servers were not production systems, but they did have the latest steppings and firmware. Given that the clocksource watchdog is a continual diagnostic check with frequency of twice a second, there is no need to rush it when the system is under heavy load. Therefore, when high clocksource read latencies are detected, suspend the watchdog timer for 5 minutes. Signed-off-by: Feng Tang Acked-by: Waiman Long Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Feng Tang Signed-off-by: Paul E. McKenney --- kernel/time/clocksource.c | 45 +++++++++++++++++++++++++++----------- 1 file changed, 32 insertions(+), 13 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index fc486cd..91836b7 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -387,6 +387,15 @@ void clocksource_verify_percpu(struct clocksource *cs) } EXPORT_SYMBOL_GPL(clocksource_verify_percpu); =20 +static inline void clocksource_reset_watchdog(void) +{ + struct clocksource *cs; + + list_for_each_entry(cs, &watchdog_list, wd_list) + cs->flags &=3D ~CLOCK_SOURCE_WATCHDOG; +} + + static void clocksource_watchdog(struct timer_list *unused) { u64 csnow, wdnow, cslast, wdlast, delta; @@ -394,6 +403,7 @@ static void clocksource_watchdog(struct timer_list *unu= sed) int64_t wd_nsec, cs_nsec; struct clocksource *cs; enum wd_read_status read_ret; + unsigned long extra_wait =3D 0; u32 md; =20 spin_lock(&watchdog_lock); @@ -413,13 +423,30 @@ static void clocksource_watchdog(struct timer_list *u= nused) =20 read_ret =3D cs_watchdog_read(cs, &csnow, &wdnow); =20 - if (read_ret !=3D WD_READ_SUCCESS) { - if (read_ret =3D=3D WD_READ_UNSTABLE) - /* Clock readout unreliable, so give it up. */ - __clocksource_unstable(cs); + if (read_ret =3D=3D WD_READ_UNSTABLE) { + /* Clock readout unreliable, so give it up. */ + __clocksource_unstable(cs); continue; } =20 + /* + * When WD_READ_SKIP is returned, it means the system is likely + * under very heavy load, where the latency of reading + * watchdog/clocksource is very big, and affect the accuracy of + * watchdog check. So give system some space and suspend the + * watchdog check for 5 minutes. + */ + if (read_ret =3D=3D WD_READ_SKIP) { + /* + * As the watchdog timer will be suspended, and + * cs->last could keep unchanged for 5 minutes, reset + * the counters. + */ + clocksource_reset_watchdog(); + extra_wait =3D HZ * 300; + break; + } + /* Clocksource initialized ? */ if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || atomic_read(&watchdog_reset_pending)) { @@ -523,7 +550,7 @@ static void clocksource_watchdog(struct timer_list *unu= sed) * pair clocksource_stop_watchdog() clocksource_start_watchdog(). */ if (!timer_pending(&watchdog_timer)) { - watchdog_timer.expires +=3D WATCHDOG_INTERVAL; + watchdog_timer.expires +=3D WATCHDOG_INTERVAL + extra_wait; add_timer_on(&watchdog_timer, next_cpu); } out: @@ -548,14 +575,6 @@ static inline void clocksource_stop_watchdog(void) watchdog_running =3D 0; } =20 -static inline void clocksource_reset_watchdog(void) -{ - struct clocksource *cs; - - list_for_each_entry(cs, &watchdog_list, wd_list) - cs->flags &=3D ~CLOCK_SOURCE_WATCHDOG; -} - static void clocksource_resume_watchdog(void) { atomic_inc(&watchdog_reset_pending);