On Wed, Feb 11, 2009 at 02:28:40PM -0500, Silas Boyd-Wickizer wrote:
> > With 16 logical CPUs, in this configuration you'll find your CPU load
> > to be 1/16th of the theoretical maximum + overhead. Your report of 10%
> > is about right.
>
> The system has 16 physical execution units: four quad core AMD
> Opterons. In the configuration I described, 90% of total cycles
> are unused.
Yes, but in this configuration, 1 CPU is pegged, and the others are idle,
actually the others are working baout as hard combined, so that's where
you get the ~10%.
> > What exactly are you trying to measure with this "benchmark"?
>
> I'm measuring how many emails Postfix can deliver per-sec to some
> number of virtual aliases. I'm not interested so much in the
> absolute throughput performance, but in the reasons for the
> performance.
Why is this an interseting measurement? In practice, your performance will
be at least a factor of 10 (more likely 30-100) lower, once you add
real disk latency, and other real loads.
> > No realistic configuration has the same critical resource, and you'll
> > run out of disk I/O throughput or CPU first depending on how CPU hungry
> > your content-filters are.
>
> I understand this.
>
> > If you really are planning to host all spools in RAM disk, and need more
> > than 3000 msgs/sec, I am most curious what use-case motivates this design
> > and performance requirement.
>
> I don't have a real use-case in mind.
This benchmark is essentially meaningless, it proves that Postfix
switching won't be a problem util you reach 3000 msgs/sec. Since
your real loads will be much lower, you don't have to worry about it.
--
Viktor.
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