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SubjectRe: [PATCH] HZ change for ix86
On Sat, 9 Jan 1999, Horvath Karoly wrote:

> On Fri, Jan 08, 1999 at 09:14:14AM -0500, Richard B. Johnson wrote:
> > There seems to be a general misinformation about what the HZ value is.
> > I will "simplicate and add lightness".
>
> still darkness here....
>
> > However, if your code is doing:
> >
> > UncompressFonts(...........);
> > ReadAudioFromDsp(...........);
> > ConvolveImageData(..........);
> >
> > you don't want the CPU taken away until you are done.
>
> We can't prevent the kernel from taking away the CPU - and a higher HZ value
> helps us get back the CPU as soon as possible.

If we don't do blocking system calls, we don't lose the CPU until our
time-slice is up.

Once you lose the CPU, you may lose it for N time slices because there
are N computable tasks that will get it before you get it back. This is a
multitasking operating system with many more tasks than just yours. You
get it CPU back when it's your turn, not the next timer-tick.

If N tasks are CPU bound, you sure want a long time-slice before the
CPU gets stolen from you.

>
> > doesn't produce visual effects. The higher the HZ value, the more
> > often the CPU gets stolen from the interactive user.
>
> Why is that a problem? Here is an example:
> You earn 1000$ a month. Your boss decides to pay you not monthly but weekly,
> and you begin to complain that you only earn 250$.

Not accurate.



Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.1.131 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.
Wisdom : It's not a Y2K problem. It's a Y2Day problem.



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