kern.timecounter.hardware change on the fly

[Ireneusz Pluta]

Hi all,

is it safe to change kern.timecounter.hardware on a busy production system on the fly? Or I better 
schedule a downtime to do that?

It seems I got a bad current selection, somehow, probably as an effect of leaving /etc/sysctl.conf 
contents of early experimental setup stage of this machine.

$ sysctl -a | grep timecounter
kern.timecounter.tick: 1
kern.timecounter.choice: TSC(-100) HPET(900) ACPI-fast(1000) i8254(0) dummy(-1000000)
kern.timecounter.hardware: i8254
kern.timecounter.stepwarnings: 0
kern.timecounter.tc.i8254.mask: 65535
kern.timecounter.tc.i8254.counter: 23813
kern.timecounter.tc.i8254.frequency: 1193182
kern.timecounter.tc.i8254.quality: 0
kern.timecounter.tc.ACPI-fast.mask: 16777215
kern.timecounter.tc.ACPI-fast.counter: 4619803
kern.timecounter.tc.ACPI-fast.frequency: 3579545
kern.timecounter.tc.ACPI-fast.quality: 1000
kern.timecounter.tc.HPET.mask: 4294967295
kern.timecounter.tc.HPET.counter: 1703441786
kern.timecounter.tc.HPET.frequency: 14318180
kern.timecounter.tc.HPET.quality: 900
kern.timecounter.tc.TSC.mask: 4294967295
kern.timecounter.tc.TSC.counter: 2720513805
kern.timecounter.tc.TSC.frequency: 2266656152
kern.timecounter.tc.TSC.quality: -100
kern.timecounter.smp_tsc: 0
kern.timecounter.invariant_tsc: 1

This setting seems to affect what is generally described here: 
http://archives.postgresql.org/pgsql-admin/2011-01/msg00059.php and this is the primary reason I 
want to change.

Should I switch to HPET or ACPI-fast?