Le 2010-10-15 03:17, Bas Smeelen a écrit :
From: Martin Turgeon [mailto:free...@optiksecurite.com]
To: freebsd-questions@freebsd.org
Sent: Thu, 14 Oct 2010 21:46:13 +0200
Subject: How is CPU usage calculated?
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 :)
Yes if you have multiple cpu's, cores or hyperthreading than each unit can be
used up to 100%
Mysql has multiple threads, you can check with top -P to see the multiple cores
and when top is running give the command H (capital H) to see the threads of
each process
Thanks for your reply!
I didn't knew about -H to show individual threads, but my problem isn't
there. My problem is that the summary printed in the first lines doesn't
match the total of the process detailled under the summary. For example,
I have a user CPU usage est 83.1% in the summary, but the only process
worth mentionning in the list is mysqld that is taking 255.52% WCPU.
That's far less than half the "CPU power" but 83% is far more. It's that
difference that I don't understand.
How is this possible?
Martin
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