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SubjectRe: Can and should the kernel HZ value be changed?

On Wed, 6 Jan 1999, Pavel Machek wrote:

> Linux has some problems with scheduling:
>
> If you access disks or do other similar tasks (login), and there's
> background process running, you get scheduled at next timer tick - ie.
> 10ms later. This way, I was able to "feel" background while(1);
> processes on my 486/16. I'm currently running some tests (find / in
> fact), to see if this canbe measured in addition to 'felt'.

no. you get scheduled immediately. You can 'feel' it with a background
process running because starting up a shell is a multi-millisec CPU
excercise even on fast boxes and fully cached, and processes do not start
up with excessive priorities. (see how childs and parents share p->counter
in fork.c) Thus the login is timesharing with the background process.

but after a few seconds, your shell gathers enough 'interactiveness
priority' to not hang when you hit 'Enter'.

-- mingo

ps. you can also renice the background process, in that case even right
after fork() the typical shell process has higher priority than a CPU
eater. 'renice' is your friend.


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