[GIT PULL clocksource] Clocksource watchdog commits for v5.17

[GIT PULL clocksource] Clocksource watchdog commits for v5.17

[Paul E. McKenney]

Hello, Thomas,

This pull request contains a pair of changes, both courtesy of Waiman
Long:

1.	Avoids accidental unstable marking of clocksources by rejecting
	clocksource measurements where the source of the skew is the delay
	reading reference clocksource itself.  This change avoids many
	of the current false positives caused by epic cache-thrashing
	workloads.

	https://lore.kernel.org/lkml/20211118191439.1000012-2-longman@redhat.com/

2.	Reduces the default clocksource_watchdog() retries to 2, thus
	offsetting the increased overhead due to #1 above rereading the
	reference clocksource.

	https://lore.kernel.org/lkml/20211118191439.1000012-3-longman@redhat.com/

These have been subjected to the kbuild test robot and -next testing,
and are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git clocksource

for you to fetch changes up to 1a5620671a1b6fd9cc08761677d050f1702f910c:

  clocksource: Reduce the default clocksource_watchdog() retries to 2 (2021-11-30 17:22:29 -0800)

----------------------------------------------------------------
Waiman Long (2):
      clocksource: Avoid accidental unstable marking of clocksources
      clocksource: Reduce the default clocksource_watchdog() retries to 2

 Documentation/admin-guide/kernel-parameters.txt |  4 +-
 kernel/time/clocksource.c                       | 52 ++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 12 deletions(-)

[tip: timers/core] Merge branch 'clocksource' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into timers/core

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     35e13e9da9afbce13c1d36465504ece4e65f24fe
Gitweb:        https://git.kernel.org/tip/35e13e9da9afbce13c1d36465504ece4e65f24fe
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 10 Jan 2022 13:57:17 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 10 Jan 2022 13:57:17 +01:00

Merge branch 'clocksource' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into timers/core

Pull clocksource watchdog updates from Paul McKenney:

 - Avoid accidental unstable marking of clocksources by rejecting
   clocksource measurements where the source of the skew is the delay
   reading reference clocksource itself.  This change avoids many of the
   current false positives caused by epic cache-thrashing workloads.

 - Reduce the default clocksource_watchdog() retries to 2, thus offsetting
   the increased overhead due to #1 above rereading the reference
   clocksource.

Link: https://lore.kernel.org/lkml/20220105001723.GA536708@paulmck-ThinkPad-P17-Gen-1
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