Re: PSA: Clock drift and pkgin

[mlelstv%serpens.de@localhost (Michael van Elst)]

mouse%Rodents-Montreal.ORG@localhost (Mouse) writes:

>> Modern hardware could easily do 100kHz.

>Not with curren^Wat least one moderately recent NetBSD version!

>At work, I had occasion to run 9.1/amd64 with HZ=8000.  This was to get
>8-bit data pushed out a parallel port at 8kHz; I added special-case
>hooks between the relevant driver and the clock (I forget whether
>softclock or hardclock).  It worked for its intended use fairly
>nicely...but when I tried one of my SIGALRM testers on it, instead of
>the 100Hz it asked for, I got signals at, IIRC, about 77Hz.


Scheduling and switching userland processes is heavy. For a test
try to schedule kernel callouts with high HZ values. That still
generates lots of overhead with the current design but you should
be able to go faster than 8kHz.