linux

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Kasper Pedersen a386b5af8e time: Compensate for rounding on odd-frequency clocksources

When the clocksource is not a multiple of HZ, the clock will be off.  For
acpi_pm, HZ=1000 the error is 127.111 ppm:

The rounding of cycle_interval ends up generating a false error term in
ntp_error accumulation since xtime_interval is not exactly 1/HZ.  So, we
subtract out the error caused by the rounding.

This has been visible since 2.6.32-rc2
	commit a092ff0f90cae22b2ac8028ecd2c6f6c1a9e4601
	time: Implement logarithmic time accumulation
That commit raised NTP_INTERVAL_FREQ and exposed the rounding error.

testing tool: http://n1.taur.dk/permanent/testpmt.c
Also tested with ntpd and a frequency counter.

Signed-off-by: Kasper Pedersen <kkp2010@kasperkp.dk>
Acked-by: john stultz <johnstul@us.ibm.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2010-10-21 17:30:05 +02:00

clockevents.c

clockevent: Don't remove broadcast device when cpu is dead

2010-01-18 14:44:50 +01:00

clocksource.c

clocksource: Add __clocksource_updatefreq_hz/khz methods

2010-07-27 12:40:55 +02:00

jiffies.c

clocksource: Cleanup clocksource selection

2009-08-15 10:55:46 +02:00

Kconfig

time: Kill off CONFIG_GENERIC_TIME