Re: Nice processes on Unix

On Jun 6, 7:37 am, Madhu <enom...@xxxxxxxx> wrote:

`loadavg' is a measure of contention -- [see manpage definition below]
loosely it is the number of processes trying to run simultaneously
(contending for CPU) or waiting for IO (contending for Disk). Someone
from google once told me that if this number is greater than 1 "your
system is in trouble", as the system is overloaded.

I'm not sure how much it varies between implementations, but
traditionally, and simplifying somewhat, the load average is the
number of processes which are not waiting for anything other than I/O
in order to run (ie this does not count processes which are waiting
for you to type something, say).

Thus a load average less than or equal to the number of cores in the
system means that everything is getting CPU time that wants it
(processes may still be starving for I/O of course).

In particular, what is a "bad" load average scales as the number of
cores: for many years of course Unix systems all had a single core,
but nowadays very many systems have more than one of course. This
took me a while to get used to, but now I always check the number of
cores before panicking at a load of 25 or something...

(And "cores" is not correct: on systems such as Sun's CMT machines the
number of interest is the number of virtual processors, which is some
multiple of the number of cores (4 or 8, depending on generation I
think).)

-tim

--tim
.

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