Compaq 350MHz PII + Linux performance degradation of 500% after a while: normal behaviour?

Rolf Fokkens (rolf@flits102-126.flits.rug.nl)
Tue, 13 Apr 1999 20:34:14 +0200

If have two Compaq 350MHz PII machines. They both show a drastic
performance degradation after running a while. This performance
degradation vanishes after a reboot. These are the circumstances when
the performance is bad:
* About 60 processes with a load of 0.1 or less
* More than 64 MB memory (one has 128MB, the other has 192MB)
* No swap space used
* Almost all memory used; (mostly for buffering, about 50MB is needed
for the processes)
* The performance degradation seems to be purely CPU related (mpg123
decoding to /dev/null runs at about 100% CPU but takes about 5 times
longer to complete)

I have no Idea what's going on, I can only guess, like:
* Maybe the memory above 64M is not cachable (like plain pentium chips)
* Maybe the CPU gets warm and the clock is slowed down te prevent damage
(although the CPU is mostly HALTing)
* ...

Now I have four questions to you people:
* This performance degradation seems important to me, is it?
* What's going on (the hard question) ?
* Have others noticed this performance degradation too?
* Can others reproduce this?

I have to admit that I haven't investigated this thoroughly myself, but
if this is a problem it's not only my problem, so your experience with
this important.

Rolf

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