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Re: high load average



On Thu, Mar 08, 2001 at 10:55:10PM -0800, kmself@ix.netcom.com wrote:
> on Tue, Mar 06, 2001 at 11:21:07AM -0600, Dave Sherohman (esper@sherohman.org) wrote:
> > You have the notation correct, but load average and CPU utilization are not
> > directly related.  Load average is the average number of processes that are
> > waiting on system resources over a certain time period; they could be waiting
> > for CPU, for I/O, or for other resources.

> It *is* CPU.  These are processes in the run queue.  A process blocked
> for I/O or another resource is blocked, not runnable

OK, now I'm confused...

My statements were based on my memory of a thread from last May (was it
that long ago?) on this very list titled "(ot) What is load average?".
Checking back on the messages I saved from that conversation, I see a
one from kmself@ix.netcom.com stating that load average is

| Number of processes in the run queue, averaged over time.  Often
| confused with CPU utilization, which it is not.

Load average either is CPU or it isn't, right?  So you can't have been
correct both times.  Now, you may have been wrong last year and since
realized that it's more CPU-related than you had thought, but (aside from
this thread's original question describing a situation with a long-term
consistent load average of 2.00 and low-to-no CPU utilization) last
May's thread also included a message from jjlupa@jamdata.net stating that

] It is the average number of processes in the 'R' (running/runnable) state
] (or blocked on I/O).

and

] The load average is most directly related to CPU.  Two CPU-intensive
] processes running will result in a load average of 2, etc.  But I/O
] intensive processes spend so much time active that they can drive up the
] load average also.  In addition if more than one process is blocked on I/O
] then the load average will go up very quickly, as both processes count
] toward the load even if only one can access the disk at a time.

Based on my observations of load and CPU readings on my boxes and the
messages from last May that I quoted above, I'm inclined to maintain
my earlier statement that processes waiting on any resource (not just
CPU) contribute to load.  But, if that's not the case, I'm willing to
be corrected.

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