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| author | Paul E. McKenney <paulmck@kernel.org> | 2022-12-06 19:36:10 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2023-01-03 20:43:45 -0800 |
| commit | c37e85c135cead4256dc8860073c468d8925c3df (patch) | |
| tree | d7871da13c5a39e5adff5a455935260f5502c48a /kernel/time/Kconfig | |
| parent | beaa1ffe551c330d8ea23de158432ecaad6c0410 (diff) | |
| download | linux-c37e85c135cead4256dc8860073c468d8925c3df.tar.gz | |
clocksource: Loosen clocksource watchdog constraints
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 <riel@surriel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/time/Kconfig')
| -rw-r--r-- | kernel/time/Kconfig | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index a41753be1a2bf2..bae8f11070befe 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 μs)" 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! endmenu endif |