Re: Scheduler ( was: Just a second ) ...

[Davide Libenzi]

On Mon, 17 Dec 2001, Linus Torvalds wrote:

>
> On Mon, 17 Dec 2001, Davide Libenzi wrote:
>
> > On Sat, 15 Dec 2001, Linus Torvalds wrote:
> >
> > > I just don't find it very interesting. The scheduler is about 100 lines
> > > out of however-many-million (3.8 at least count), and doesn't even impact
> > > most normal performace very much.
> >
> > Linus, sharing queue and lock between CPUs for a "thing" highly frequency
> > ( schedule()s + wakeup()s ) accessed like the scheduler it's quite ugly
> > and it's not that much funny. And it's not only performance wise, it's
> > more design wise.
>
> "Design wise" is highly overrated.
>
> Simplicity is _much_ more important, if something commonly is only done a
> few hundred times a second. Locking overhead is basically zero for that
> case.

Few hundred is a nice definition because you can basically range from 0 to
infinite. Anyway i agree that we can spend days debating about what this
"few hundred" translate to, and i do not really want to.

> 4 cpu's are "high end" today. We can probably point to tens of thousands
> of UP machines for each 4-way out there. The ratio gets even worse for 8,
> and 16 CPU's is basically a rounding error.
>
> You have to prioritize. Scheduling overhead is way down the list.

You don't really have to serialize/prioritize, old Latins used to say
"Divide Et Impera" ;)

- Davide