numbers don't lie ...

[Kris Kennaway]

On Thu, Sep 14, 2006 at 02:13:55PM -0400, Gary Corcoran wrote:
> Mike Meyer wrote:
> >In <45099123.4000500 at rcn.com>, Gary Corcoran <gcorcoran at rcn.com> 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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