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H A D | Kconfig | c37e85c1 Tue Dec 06 21:36:10 CST 2022 Paul E. McKenney <paulmck@kernel.org> 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>
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H A D | clocksource.c | c37e85c1 Tue Dec 06 21:36:10 CST 2022 Paul E. McKenney <paulmck@kernel.org> 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>
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