How is system load determined?

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# 1  
Old 12-07-2001
How is system load determined?


I'm wondering what factors are used to determine the "system load"

Where can i look to get more information on this?

# 2  
Old 12-07-2001
Found it

system load is the average length of the processor queue.
# 3  
Old 12-08-2001
Re: Found it

Originally posted by Patrick_Morris
system load is the average length of the processor queue.
I would be interested to know where you found that particular language. The man page for uptime says
the average number of jobs in the run queue
which is very close to your language. I encountered many cases where this didn't seem to jibe with reality so I took a peek at the source code.

Rather than looking at the run queue, the load is actually computed by scanning the proc table. A process is counted if
  • it is runnable (in the run queue)
  • if it is running (in a cpu)
  • if it sleeping with a priority lower than PZERO

That last one is intended to cover processes that are waiting for disk i/o to complete. And the load is divided by the number of cpu's.
# 4  
Old 12-11-2001
System Load Average (SLA). It is important to note that the SLA can only be used as a rough indicator as it does not take scheduling priority into account . It also counts as runnable all jobs waiting for disk I/O, including NFS I/O. However, uptime is a good place to start when trying to determine whether a bottleneck is CPU or I/O based.
The extract above is from this paper..... CLICK HERE.
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