Re: [opensuse] top Load average figures


----- Original Message -----
From: "Hylton Conacher (ZR1HPC)" <hyltonconacher@xxxxxxxxx>
To: "OpenSUSE" <opensuse@xxxxxxxxxxxx>
Sent: Thursday, November 06, 2008 3:02 PM
Subject: Re: [opensuse] top Load average figures


2008/11/6 Per Jessen <per@xxxxxxxxxxxx>:
Carlos E. R. wrote:

root@Moria:~ # cat /proc/cpuinfo
processor : 0
cpu model : NEC VR4122 V7.2
BogoMIPS : 165.88
wait instruction : no

Carlos, that is not a small machine - this one is:

# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 4
model : 3
model name : 486 DX/2
[snip]
bogomips : 32.97

Tnx all.

So basically its 1.00 per core so a dual core would need to get to
load of 2.00 to fully be using the CPU. Carlos, in your case either
the CPU has 4 cores and is being overworked or I am mis-understanding
summat.

-----------------------------------------------

Sorta-kinda-not-really :)

It's also possible to have load average of 20 on a
single core cpu and yet have the entire system be
perfectly idle.

Load average is the number of processes waiting to run.
Nothing more. Typically the only time the load average
exceeds 1.0 per cpu core, is when you are feeding it
more work than the system can keep up with.

But that's only _typically_. Cpus have to wait on ram
and hd and other forms of i/o, and sometimes they have
to wait on other cpu's in multi-cpu boxes. And processes
in turn have to wait on cpus. Processes could be stuck,
scheduled to run now but unable to run because of various
other delays and blockages in the system which don't have
to be "The cpu is already maxxed out and just can't work
fast enough to get to me immediately"

One common situation is a single buggy process that
is really in a sort of stuck idle state, perhaps waiting
on some hardware event that will never come, or perhaps
just internally purely software glitch. But, it's in
in the run queue in running state, not sleeping or waiting
like most others that are "running", and so it adds exactly
1.0 to the load average, and since it's stuck forever unless
you manually come along and kill it, you basically have
a normally loaded system, nothing wrong or waiting or
overloaded anywhere with a load average exceeding 1.0
(on a single cpu) because as long as that buggy process
is there, your load average is just artificially inflated
by 1.0 across the board at all times. It's probably really
only say, 0.03, just about quiescent, yet load average would
say 1.03, which looks like slightly overloaded unless you
realize all I just said and what load average actually is,
and is not.

It IS a useful diagnostic or metric or indicator, but
it's not really much all by itself. Like one clue out of
may. Not garanteed to mean anything by itself, but
useful in context with all other clues and observations.

Like if a room is dark, that only tells you that the room
is dark. It doesn't necessarily mean there is some problem
with the room lights or tell you anything about why the
room is dark. Maybe the power bill is overdue, maybe you
shut the lights off because it's night and you want to sleep,
maybe the bulb broke, maybe all lights and windows have been
painted over by your practical joker friends, etc etc etc.

However from a different direction, it is possibly a clue
into some other problem. "My plants are all dead!" "Well
we have observed that the room is always dark."
Which may then lead you to investigate possible reasons
the room is dark. But the problem was really the plants,
the darkness was just a clue and only meaningful in the
context of the problem with the plants.

Smilarly, load average may or may not actually indicate
any problem all by itself. But, if your system is suddenly
very slow compared to normal, AND you then see that your
load average is at the same time very high compared to
normal, THEN load average is a clue hinting at some possible
causes for the slow down in that particular case.

--
Brian K. White brian@xxxxxxxxx http://www.myspace.com/KEYofR
+++++[>+++[>+++++>+++++++<<-]<-]>>+.>.+++++.+++++++.-.[>+<---]>++.
filePro BBx Linux SCO FreeBSD #callahans Satriani Filk!

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