[clug-talk] understanding top output

s. keeling keeling at spots.ab.ca
Thu Nov 18 15:13:28 PST 2004

Incoming from smagnuson at forzani.com:
> Does anyone here know where to find a detailed description of the
> "load average" field in top?  What is used to determine these numbers?

man top, then "/ load":

     This line displays the time the system has been  up,  and  the  three  load
     averages  for the system.  The load averages are the average number of pro­
     cess ready to run during the last 1, 5 and 15 minutes.  This line  is  just
     like  the  output  of  uptime(1).  The uptime display may be toggled by the
     interactive l command.

So, assuming the CPU's job is to give some percent of CPU time to each
process that's waiting for CPU time, the load averages tell you how
many processes the CPU has to keep happy.

Load averages aren't everything, though.  All the resources on the
machine need to be managed.  A process that's reading from or writing
to disk won't need much CPU, but disk accesses are slow.  You also
need to allocate and free buffers, page in and out processes to and
from swap (also slow), & etc.  Given enough RAM, you can eliminate the
need for swap.  Given faster disks (a la striped RAID storage) you can
boost disk I/O throughput.

Any technology distinguishable from magic is insufficiently advanced.
(*)    http://www.spots.ab.ca/~keeling      Please don't Cc: me.
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