Re: polling interval

On Tue, 15 Oct 2024 11:20:49 +0100
void <void@f-m.fm> wrote:

> On Tue, Oct 15, 2024 at 10:51:20AM +0100, void wrote:
> 
> >I'll next try setting kern.hz to -1
> 
> setting it to -1 returns a kern.hz value of 100 on reboot
> setting it to 0 returns the kern.hz_min value of 8
> setting it to 1 and the kern.hz_min value to 1 still returns 8.

-1 means "choose default".
Behaviors for 0 and 1 would be because HZ_MINIMUM is defined as 8 in
sys/sys/time.h, causing to clip to 8.


> kern.hz=8 and kern.hz=100 gave the same numbers on bandwidth tests.
> -- 

Maybe kern.hz=100 gives enough time (per tick) and kernel returns near
the time even for kern.hz=8, disposing remaining time of the tick.

# There was an abandoned review D40045 to reuse the disposed remaining
# (fragmented) ticks. [1]


And forgot tomention in my previous post. kern.hz for VMs (recognized
as running on VM by FreeBSD kernel) is 100, as the default is HZ_VM.

HZ and HZ_VM is defined as 1000 and 100 respectively, if not defined
elsewhere. And if HZ_VM alone is not defined elsewhere, it is
defined as HZ.

These are because you see default kern.hz=100 on your VMs.

[1] https://reviews.freebsd.org/D40045


-- 
Tomoaki AOKI    <junchoon@dec.sakura.ne.jp>