Difference in CPU time with and without ePN

Thomas Guyot-Sionnest thomas at zango.com
Tue Jan 8 17:32:51 CET 2008


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If anyone's interested here's what ePN versus pure Perl plugins can
looks like on the server's CPU load. This is on a dual proc
(multi-threaded == 4 proc) server with hardware SCSI raid
(battery-backed write-back) and 2GiB of RAM.

The server is almost doing 1000 active check/minutes spread on nearly
100 hosts (Nagios 2.7). In the attached graph you can see the server
load as I changed the settings of one Perl plugin that runs 28 times
every minute. There's two drops:

1. At the very beginning I removed the "/usr/bin/perl " in the
checkcommand definition. The ePN compilation was failing so the file was
likely still being recompiled at every run. The drop in user time seems
to be from the plug-in not running (but still being compiled).

2. After the week-end, the 2nd drop shows the drop when I fixed the
plug-in compilation. At that time the plugin was running again but not
being recompiled at each run, which caused a raise in user time and a
nice drop in system time.

This graph clearly shows that ePN is a must for any big system that rely
heavily on Perl plugins. The difference you see here is caused by only
28 check out of nearly 1000.

The CPU data is gathered every minutes trough SNMP counters and properly
divided according to the number of CPUs.

- --
Thomas
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