How is CPU usage calculated?
Martin Turgeon
freebsd at optiksecurite.com
Thu Oct 14 20:46:11 UTC 2010
Hi list!
I did a strange observation yesterday night. The CPU usage reported by
top doesn't match what is indicated under it. I was seeing around 80-90%
user, 5% system, 1% interrupt and 10% idle. But the process details
under it doesn't match. mysqld was taking around 250% (WCPU) with a few
httpd processes at 1-2%. The system is running GENERIC 8.0-REL on a Xeon
E5630 (quad core with hyperthreading so 8 CPUs). MySQL and Apache each
have their own jail (I don't think it will matter but just in case)
I understand why the mysqld process take more than 100% but how can I
know what's taking the rest? Why doesn't the total user CPU usage match
the total of the CPU usage of each process? Is there a link with
hyperthreading?
There sure is a logical answer and I would really like to know it :)
Thanks in advance,
Martin
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