Re: How can this 'top' command output make sense? Load over 7 and total CPU use ~5%
- From: Glen Barber <glen.j.barber@xxxxxxxxx>
- Date: Sun, 24 May 2009 05:47:12 -0400
On Sun, May 24, 2009 at 5:07 AM, Matthew Seaman wrote:
I thought, if it was a dual-core for example, a load average of 1.00
would indicate 50% CPU utilization overall (1 process using only 1
core)[1]. 2.00 on a dual-core would be 100%, 3.00 on a dual-core
would be 100% utilization, and always 1 process in the wait queue, and
so on.
It seems both ways have been used in different OSes, which is confusing.
A quick test of a single threaded process that will spin one CPU on a
multi-core FreeBSD box shows the value is /not/ scaled by the number of
cores.
Meaning a load average of 1.00 on a single-core versus dual-core means
the same thing? I can't tell if you said what I said (or meant) with
different wording, or if you said the opposite. :-)
Which means that the LA the OP was talking about is actually a lot less
alarming
than it originally appears. It's clear from the top output that his machine
has at least 8 cores, so a LA of 7 is really not very heavily loaded.
So in this situation, he has 1 core idle all of the time, correct?
Does this affect the load average though? My understanding was that
if the CPU cannot immediately process data, the data gets put into the
wait queue until L2 Cache (then RAM, etc, etc) returns the data to be
processed.
Yes it does: when a process is on the CPU and blocked waiting for IO
it does not necessarily yield the CPU to another process. It depends on
timescales -- obviously if the CPU will have to wait milliseconds for data
it makes no sense to block other processes. Waiting a few microseconds is
a different matter though: it might take that long to load up L2/L3 cache
with that processes' working data, so yielding the CPU for that sort of
delay
would mean the process never got run, which is counter productive... It
helps if the working set is already in the L3 cache -- so having the correct
amount[*] of cache RAM available is an important design criterion.
Makes sense.
--
Glen Barber
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- References:
- How can this 'top' command output make sense? Load over 7 and total CPU use ~5%
- From: Yuri
- Re: How can this 'top' command output make sense? Load over 7 and total CPU use ~5%
- From: Matthew Seaman
- Re: How can this 'top' command output make sense? Load over 7 and total CPU use ~5%
- From: Glen Barber
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