Re: top stack (l)users for 2.5.69

Jörn Engel
2003-05-07T17:29:19Z

On Wed, 7 May 2003 10:18:29 -0700, Davide Libenzi wrote:
> On Wed, 7 May 2003, [iso-8859-1] Jörn Engel wrote:
>
> > It also matters if people writing applications for embedded systems
> > have a fetish for many threads. 1000 threads, each eating 8k memory
> > for pure existance (no actual work done yet), do put some memory
> > pressure on small machines. Yes, it would be possible to educate those
> > people, but changing kernel code is more fun and less work.
>
> I'm afraid I do not agree with both your sentences. Changing a *working
> kernel* code is definitely not much fun and not really less work if your
> target is the per-cpu kernel stack. You'll completely lose kernel
> preemption and this is really bad since many paths inside the kernel are
> easily preemptable. The design and the code of the kernel will become more
> complex (and slow) and even people that are correctly programming it are
> going to pay the price. No thanks, I'd say screw you thread maniacs ...

I'm not sure if I got you wrong, or vice versa. Either way, some
definitions first.
Process Stack == the traditional per-process kernel stack
Interrupt Stack == a dedicated per-CPU stack for interrupts only
CPU Stack == all kernel data on a per-CPU stack

Not for anything would I want a CPU Stack. At first thought, this is
impossible, but in reality it is just ugly beyond anything I could
bear.

An Interrupt Stack is a very good thing. I know PPC machines with 125
Interrupt lines (3 for cascading) that could theoretically all happen
at once. That alone demands for a stack size well above 8k and having
this per process is just a bad design. But that is another issue.

The real Process Stack without the interrupt overhead should not need
to be bigger than 4k. It currently is for all platforms I know about,
s390 has even 16k. This is the point of my regular allyesconfig
compilations and postings.

Do you still disagree? Then I must have misread your mail.

Jörn

--
Do not stop an army on its way home.
-- Sun Tzu