[CentOS] Load Average

Rodrigo Barbosa rodrigob at suespammers.org
Thu Mar 2 16:31:41 UTC 2006

Hash: SHA1

Heavy quotation editing ahead :)

On Wed, Mar 01, 2006 at 11:05:59PM -0500, Sam Drinkard wrote:
> On Wed, 2006-03-01 at 20:49 -0600, Les Mikesell wrote:
> I was more curious than anything as to what would constitute heavy or 
> moderate loads. 

I really depends.

The load itself is only part of the equation. The process scheduler is
also an important part. I once tested Riel's "fair scheduler" on a
single processor P2 machine, with a nice fork bomb running. As long as
I was using a different user than the one running the fork bomb, I would
barely notice any problems (load was 250+).

On the other hand, I have seen places with a single high I/O process
would put a 4-way system on its knees.

It is important to notice that a Sparc system would not get all locked
up due to IRQs the say a PC does. That might explain why the load on
that system was so high and still usable.

Bottom line, machine load average is good data, but still only part of
the equation. Having a good process scheduler can make a huge difference,
but be sure to have the one that is more adequate to your use, if you
decide to play with it.

> This evening, while there were processes active, I did a few tests, one of
> which was the hdparm -t, and I was quite shocked to see how low the thruput
> really was, albeit cached.  Results were like 18mb/sec where as a few other
> times during a lighter loading, I/O was what I consider respectable, at 160 +/-
> mb/ 3 seconds., or approximately 54mb/sec.  

That is I/O, all right.

> System was *very* slow to log me out, 

Probably cause it was saving configurations and such.

> but was about normal when I logged back in.  

Mostly cached and pre-loaded.

> Since the machine only has a single
> 200gb disk, I suspect part of the sluggishness comes from a bottlenecked disk
> I/O, just based on so many processes actually in swap.

You can always use "iostat" to see what is happening.

- -- 
Rodrigo Barbosa <rodrigob at suespammers.org>
"Quid quid Latine dictum sit, altum viditur"
"Be excellent to each other ..." - Bill & Ted (Wyld Stallyns)

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