Re: Why was the timehands_count sysctl added?

On Sat, Oct 09, 2021 at 09:41:28PM +0200, Sebastian Huber wrote:
> Hello,
> 
> I synchronize currently the port of the FreeBSD timecounters to RTEMS and
> came across a change in 2019 which I do not understand. Some time ago the
> timehands were reduced from 10 to two:
> 
> https://reviews.freebsd.org/D7302
> 
> In 2019 this changed again to be up to 16:
> 
> https://reviews.freebsd.org/D21563
This review did not changed it back to 16, the default value is still 2.
It allows to bump the number of used timehands, but normally systems run
with only 2.

> 
> The corresponding sysctl is not documented:
> 
> https://www.freebsd.org/cgi/man.cgi?query=timecounters&sektion=4
> 
> Does someone know why this sysctl to select the count of timehands was
> added? Is this a performance optimization for some systems?

To allow for experimentation, and to satisfy some requests where people
wanted to have more that 2 timehands.