Donn Miller wrote:
> Patrick Mau wrote:
> > On all Unix-like systems I know, the load average is the average mumber
> > of processes running during a given time interval. I can't see what use
> > it may have to count load for _waiting_ processes.
> >
> > I/O load is not process load, if a process waits for I/O completion it does
> > not use up its timeslice.
>
> I think we ought to re-examine the definition of load average. By
> load, we mean an actual load on the cpu, and waiting processes aren't
> really exerting a cpu load. So, by that reasoning I say waiting
> processes don't count.
In this case, the "waiting" refers to the processes waiting in the
_run_ queue, i.e., if the system wasn't so busy, they'd be running
more often instead of waiting. In a uniprocessor system, only one
process can be running at a time. When that currently running process
is swapped away from the cpu, another process from the run queue is
selected to run (which is actually an array of queues, lower indexes
meaning higher priority). Load average is the average number of
processes that are runnable, i.e., sitting in the run queue, over a
certain period of time, usually computed for the most recent 1 minute,
5 minute, and 15 minute intervals.
I think you guys are mixing up I/O wait with the run queue. The
processes are indeed waiting, but they are waiting for a chance to get
the CPU, not for someone to press a key on the keyboard or some other
external event, without which, the process could not correctly
continue until that event occurs. There is a _huge_ difference
between the two. And yes, it is a pretty good, simple indicator of
system load, and that is all it is really meant to be. If you need
something fancier, or more specific to a particular load type, you'd
need to roll your own using the abundant statistics that the kernel
keeps and makes available.
-Brian
--
Brian Dean [EMAIL PROTECTED]
SAS Institute Inc. [EMAIL PROTECTED]
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