linux-kernel - [PATCH clocksource 0/3] Reject bogus watchdog clocksource measurements

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Message-ID: <20221114232807.GA834337@paulmck-ThinkPad-P17-Gen-1>
Date:   Mon, 14 Nov 2022 15:28:07 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...a.com, neeraju@...eaurora.org,
        ak@...ux.intel.com, feng.tang@...el.com, zhengjun.xing@...el.com
Subject: [PATCH clocksource 0/3] Reject bogus watchdog clocksource
 measurements

Hello!

This series adds comments classifying bogus measurements and adds capped
exponential backoff for messages that are likely caused by overly busy
systems.

1.	Reject bogus watchdog clocksource measurements.

2.	Add comments to classify bogus measurements.

3.	Exponential backoff for load-induced bogus watchdog reads.

Changes since v1:

o	Merge the "Reject bogus watchdog clocksource measurements" [1] series
	with the "Clocksource-watchdog classification and backoff" [2] series.

o	Updated messages to indicate timer bug for too-short watchdog
	intervals based on Feng Tang feedback.

o	Added explanatory comments before error messages based on Feng
	Tang feedback.

o	Check both the reference clocksource and the clocksource under
	test to handle clocksource-internal counter wrap, based on Feng
	Tang feedback.

o	Reversed the order of the checks, so that the too-long check
	preceeds the too-short check.  This avoids too-short false
	positives due to counter wrap.

o	Simplified exponential-backoff time checks based on feedback
	from Waiman Long.

o	Updated the exponentially backed off messages to more clearly
	indicate that the counts are instances since the last printed
	message.

o	Applied Reviewed-by tags.

[1] https://lore.kernel.org/all/20221019230904.GA2502730@paulmck-ThinkPad-P17-Gen-1
[2] https://lore.kernel.org/all/20221102184001.GA1306489@paulmck-ThinkPad-P17-Gen-1/

						Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/clocksource.h |    3 +++
 b/kernel/time/clocksource.c   |   13 ++++++++++++-
 kernel/time/clocksource.c     |   33 +++++++++++++++++++++++++++------
 3 files changed, 42 insertions(+), 7 deletions(-)