In article <Pine.LNX.4.21.0001201818410.148-100000@dlang.diginsite.com>,
David Lang <dlang@diginsite.com> wrote:
>Shortly before I went and purchased $10,000 encryption co-processors for
>my SSL web servers it was not unusual to see a 5 min loadave of 30-50 (and
>one time I saw it go up to 144!!). This was on AIX quad 233 2G ram RS/6000
>servers, after I got the encryption co-processors the loadave dropped to
>5-10
Ok, before this gets out of hand, let me just clarify:
- under loads like the above, scheduling speeds MEANS ABSOLUTELY
NOTHING.
Nada. Zilch. Zero.
You aren't spending any time scheduling - you're spending all the time
COMPUTING. The high load is because you're compute-bound, and you
probably end up scheduling maybe a few hundred times a second. If that.
With a default timeslice in the 10-200 millisecond range (Linux defaults
to 200ms, and that's probably too dang long), compute-active processes
aren't really much an issue.
Basically, the situation where you have BOTH
- large number of runnable processes
AND
- lots of scheduling activity
are very rare indeed. They are rare even in threaded code, unless that
threaded code has a lot of synchronization points and a lot of
synchronous inter-thread communication.
The IBM numbers are very interesting. The cache-line optimization is an
obvious performance advantage, and has been incorporated into the recent
kernels. But I think some people think that this is a common problem,
and think that "load average" automatically equals scheduling. It isn't,
and it doesn't.
Linus
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This archive was generated by hypermail 2b29 : Sun Jan 23 2000 - 21:00:26 EST