Re: linux scheduler limitations?

Fabio Riccardi
2001-03-29T21:52:32Z

I'm using 2.4.2-ac26, but I've noticed the same behavior with all the 2.4
kernels I've seen so far.

I haven't even tried on 2.2

- Fabio

David Lang wrote:

> 2.2 or 2.4 kernel?
>
> the 2.4 does a MUCH better job of dealing with large numbers of processes.
>
> David Lang
>
> On Thu, 29 Mar 2001, Fabio Riccardi wrote:
>
> > Date: Thu, 29 Mar 2001 13:19:05 -0800
> > From: Fabio Riccardi <fabio@chromium.com>
> > To: linux-kernel@vger.kernel.org
> > Subject: linux scheduler limitations?
> >
> > Hello,
> >
> > I'm working on an enhanced version of Apache and I'm hitting my head
> > against something I don't understand.
> >
> > I've found a (to me) unexplicable system behaviour when the number of
> > Apache forked instances goes somewhere beyond 1050, the machine
> > suddently slows down almost top a halt and becomes totally unresponsive,
> > until I stop the test (SpecWeb).
> >
> > Profiling the kernel shows that the scheduler and the interrupt handler
> > are taking most of the CPU time.
> >
> > I understand that there must be a limit to the number of processes that
> > the scheduler can efficiently handle, but I would expect some sort of
> > gradual performance degradation when increasing the number of tasks,
> > instead I observe that by increasing Apache's MaxClient linit by as
> > little as 10 can cause a sudden transition between smooth working with
> > lots (30-40%) of CPU idle to a total lock-up.
> >
> > Moreover the max number of processes is not even constant. If I increase
> > the server load gradually then I manage to have 1500 processes running
> > with no problem, but if the transition is sharp (the SpecWeb case) than
> > I end-up having a lock up.
> >
> > Anybody seen this before? Any clues?
> >
> > - Fabio
> >
> >
> > -
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