Re: numbers don't lie ...

On Thu, Sep 14, 2006 at 02:13:55PM -0400, Gary Corcoran wrote:
Mike Meyer wrote:
In <45099123.4000500@xxxxxxx>, Gary Corcoran <gcorcoran@xxxxxxx> typed:
The confusing thing is that I thought 'real' time should be >= 'user' +
'sys'.
But here 'user' is much greater than 'real' for both machines! The sense
I
got from the other messages in this thread is that 'user' time is somewhat
meaningless (i.e. unreliable as a measure) in a multi-CPU and/or
hyperthreading
environment. Can you clarify?

'real' is wall clock time. 'user' and 'sys' are cpu time. If your
process gets all of some cpu, then user + sys will be the same as real
time. It's not possible to get more than all of a cpu, so that's a
maximum *per cpu*. If you have multiple cpus, the formula you want is
'real' * ncpu >= 'user' + 'sys'.

Thanks to all of you for the responses. The thing that was not clear is
that despite the printed messages, user (and sys) time are *not* measures
of time.

Yes they are, they're cumulative amount of time spent executing code
in userland or in the kernel.

Kris

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