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| author | Kasper Pedersen <kkp2010@kasperkp.dk> | 2010-10-20 15:55:15 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2010-10-21 17:30:05 +0200 |
| commit | a386b5af8edda1c742ce9f77891e112eefffc005 (patch) | |
| tree | 8a74b512d751758144b219988f60d69a5fd028f9 /kernel/rtmutex-tester.c | |
| parent | 8af3c153baf95374eff20a37f00c59a295b52756 (diff) | |
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>
Diffstat (limited to 'kernel/rtmutex-tester.c')
0 files changed, 0 insertions, 0 deletions