1
linux/kernel
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
..
debug
gcov
irq
power
time
trace
.gitignore
acct.c
async.c
audit_tree.c
audit_watch.c
audit.c
audit.h
auditfilter.c
auditsc.c
backtracetest.c
bounds.c
capability.c
cgroup_freezer.c
cgroup.c
compat.c
configs.c
cpu.c
cpuset.c
cred.c
delayacct.c
dma.c
early_res.c
elfcore.c
exec_domain.c
exit.c
extable.c
fork.c
freezer.c
futex_compat.c
futex.c
groups.c
hrtimer.c
hung_task.c
hw_breakpoint.c
itimer.c
kallsyms.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c
kfifo.c
kmod.c
kprobes.c
ksysfs.c
kthread.c
latencytop.c
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
lockdep.c
Makefile
module.c
mutex-debug.c
mutex-debug.h
mutex.c
mutex.h
notifier.c
ns_cgroup.c
nsproxy.c
padata.c
panic.c
params.c
perf_event.c
pid_namespace.c
pid.c
pm_qos_params.c
posix-cpu-timers.c
posix-timers.c
printk.c
profile.c
ptrace.c
range.c
rcupdate.c
rcutiny_plugin.h
rcutiny.c
rcutorture.c
rcutree_plugin.h
rcutree_trace.c
rcutree.c
rcutree.h
relay.c
res_counter.c
resource.c
rtmutex_common.h
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c
rtmutex.c
rtmutex.h
rwsem.c
sched_clock.c
sched_cpupri.c
sched_cpupri.h
sched_debug.c
sched_fair.c
sched_features.h
sched_idletask.c
sched_rt.c
sched_stats.h
sched.c
seccomp.c
semaphore.c
signal.c
smp.c
softirq.c
spinlock.c
srcu.c
stacktrace.c
stop_machine.c
sys_ni.c
sys.c
sysctl_binary.c
sysctl_check.c
sysctl.c
taskstats.c
test_kprobes.c
time.c
timeconst.pl
timer.c
tracepoint.c
tsacct.c
uid16.c
up.c
user_namespace.c
user-return-notifier.c
user.c
utsname_sysctl.c
utsname.c
wait.c
watchdog.c
workqueue_sched.h
workqueue.c