slapd responds very slowly when cpu has 100% usage (but actually low load)

[Antonis Christofides <anthony@itia.ntua.gr>]

Hi,

At the almost idle Dual Core machine which runs slapd, I run:

   nice sh -c 'while true; do true; done' &
   nice sh -c 'while true; do true; done' &

(i.e. I'm running this twice).  Then each of the two CPUs always has
some job to do, so both CPUs have 100% usage, but this is "nice".

Then, slapd takes too long to respond to queries.  It may take 10 or
20 seconds.  If I kill or stop one of the two dummy processes, it
replies instantly.  If I continue both dummy processes, it's back to
10 or 20 seconds.  Needless to say all machine resources seem ok; low
disk usage, lots of spare memory; and slapd is not niced.

If it's not something immediately obvious, could you help me debug it?
I've run slapd with various "-d" options but it gives me results that
I have trouble understanding.

The OS is Debian 3.1 (Sarge), with a 2.6.12 SMP Linux kernel.

-- 
Antonis Christofides
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