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a386b5af8e
mirror_ubuntu-kernels/kernel/time
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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 a092ff0f90
	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 2010-07-27 12:40:54 +02:00
Makefile time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
ntp.c ntp: Clamp PLL update interval 2010-09-09 20:48:37 +02:00
tick-broadcast.c fix comment/printk typos concerning "already" 2010-07-11 21:45:40 +02:00
tick-common.c clockevents: Convert to raw_spinlock 2009-12-14 23:55:34 +01:00
tick-internal.h clockevents: Make tick_device_lock static 2009-12-14 23:55:34 +01:00
tick-oneshot.c clockevents: Sanitize min_delta_ns adjustment and prevent overflows 2010-03-12 19:10:29 +01:00
tick-sched.c Merge branch 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-08-06 13:12:36 -07:00
timecompare.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
timeconv.c time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
timekeeping.c time: Compensate for rounding on odd-frequency clocksources 2010-10-21 17:30:05 +02:00
timer_list.c sched: Intoduce get_cpu_iowait_time_us() 2010-05-09 19:35:27 +02:00
timer_stats.c hrtimers: Convert to raw_spinlocks 2009-12-14 23:55:34 +01:00