[time-nuts] Noob question, NTP stratum 1.

[Achim Gratz]

Achim Gratz writes:
> The thing to note is that you need to boot with "nohz=off",

Tom was asking what that kernel parameter meant and does.

UNIX used to have a fixed frequency interrupt called TICK that would do
its thing HZ times per second (typically HZ=100, but later on HZ=1000 on
some systems).  Without going to deep into the details, many powqer
saving features don't really work if you wake up the CPU too often, so
something called a "tickless" Linux kernel was developed and the config
switch to use it is CONFIG_NO_HZ.  The tick interrupt is still there in
such a kernel, but it can be suppressed in order to save power.  The
kernel poarameter "nohz=off" tells the kernel to not use this facility
and hence faithfully run a kernel interrupt for each TICK.  It also
prevents the kernel from shifting the deadlines of other kernel timers
in order to create "bunches" of work, which is what I needed in this
case.

Just one reference, you can dive in from there if you need to know more:
https://stackoverflow.com/questions/9775042/how-nohz-on-affects-do-timer-in-linux-kernel


Regards,
Achim.
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