Re: linux scheduler limitations?

[David Lang]

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 <[e-mail]>
> To: [e-mail]
> 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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