Date: Sun, 24 May 2009 08:15:11 -0500 (CDT) From: Scott Bennett <bennett@cs.niu.edu> To: freebsd-questions@freebsd.org, Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: Yuri <yuri@rawbw.com> Subject: Re: How can this 'top' command output make sense? Load over 7 and total CPU use ~5% Message-ID: <200905241315.n4ODFB96007801@mp.cs.niu.edu>
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On Sun, 24 May 2009 11:57:08 +0200 (CEST) Wojciech Puchar
<wojtek@wojtek.tensor.gdynia.pl> wrote without proper attribution:
>> Look below: load over 7 and no processes take much CPU.
>
>load average is NOT sum of CPU loads.
>
>for example program reading constantly from HDD and using no CPU will add
>1 to load average.
>
>other things like net I/O etc. are calculated too. i can't explain you
>exactly how because i don't know precisely.
>
>but load average is total load not just CPU load
>
From the glossary (p. 630) of _The_Design_and_Implementation_of_the
_FreeBSD_Operating_System_ by McKusick and Neville-Neil:
load average A measure of CPU load on the system. The load average
in FreeBSD is an average of the number of processes ready to
run or waiting for short-term events such as disk I/O to
complete, as sampled once per second over the previous one-
minute interval of system operation.
In the same volume in the discussion of "Calculations of Thread Priority" by
the 4.4 BSD scheduler (p. 101), it says,
"... the *load* is a sampled average of the sum of the lengths of the
run queue and of the short-term sleep queue over the previous 1-minute
interval of system operation."
Seems pretty straightforward to me.
Scott Bennett, Comm. ASMELG, CFIAG
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