How to adjust clock frequency in FreeBSD 10.1 ?

Lena at Lena at
Fri Mar 6 13:30:42 UTC 2015

> From: Rick Thomas <rbthomas at>

>>> I?ve got a machine with a really bad clock.

Motherboards usually have several timers, not single clock.
At boot time, FreeBSD kernel assigns a number called "quality" to each timer
and chooses which timer to use.
Using some hints in /etc/device.hints, you can forbid FreeBSD kernel
to use the faulty timer.

~ $ dmesg | egrep -i 'time|clock'
Timecounter "i8254" frequency 1193182 Hz quality 0
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
acpi_timer0: <24-bit timer at 3.579545MHz> port 0x4008-0x400b on acpi0
acpi_hpet0: <High Precision Event Timer> iomem 0xfefff000-0xfefff3ff irq 0,8 on acpi0
Timecounter "HPET" frequency 25000000 Hz quality 900
atrtc0: <AT realtime clock> port 0x70-0x73 on acpi0
pmtimer0 on isa0
Timecounter "TSC" frequency 2204612489 Hz quality 800
Timecounters tick every 1.000 msec

sysctl -a | egrep -i 'time|clock' | less
kern.timecounter.choice: TSC(800) HPET(900) ACPI-fast(1000) i8254(0) dummy(-1000000)
kern.timecounter.hardware: ACPI-fast

If that doesn't help, look for TIMER_FREQ in /sys/i386/conf/NOTES .

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