Initial 6.1 questions

Danial Thom danial_thom at
Wed Jun 14 17:38:14 UTC 2006

--- Kris Kennaway <kris at> wrote:

> On Tue, Jun 13, 2006 at 12:57:38PM -0700,
> Danial Thom wrote:
> > Since everyone agrees that the load measuring
> > tools aren't all that accurate, what criteria
> was
> > used to determine that the changes made in 7
> have
> > the effect that you think they have had?
> Not by using top(1).  vmstat seems to do a
> better job of reporting CPU
> usage, but still you want to measure what the
> system can actually do,
> not how accurately it estimates its own
> performance.
> Kris

Regarding vmstat:

I'm getting the same (obviously wrong) results
from vmstat. Which is no usage. I believe I cut
and pasted a snippet which showed 6000
ints/second on em with 99.x% idle. It works fine
in UP mode, which implies that you aren't
accounting properly in SMP mode. Hopefully you
(folks) can come to terms with the fact that its
broken otherwise it will never be of any use.

Regarding testing:

My view is that you are making a big mistake if
you measure everything at the edge of
performance, which is why benchmarks lie and are
generally useless. As the bus becomes saturated,
and queues become unnaturally large, timings
change. You may be measuring how well the system
recovers from events that never happen when you
just try to "see how much you can do". For
example, as the pci bus becomes saturated I/Os
take exponentially longer, so you're not really
measuring your code. You end up measuring
properties which may be very different under
normal conditions. And if you try to optimize
your code for conditions which rarely if ever
occur, you may hose it for normal use (I'm a bit
frightened by the 7.0 em changes). 

"efficiency" is what's important. I want to know
how the machine works under normal loads, not
when its in constant recovery from overloads. I
want to run a realistic load on a machine when I
test new code, to see what effect it has on
system load. For that I need tools that work.

If your machine can push 500Mb/s at 99% load or
it can do 492Mb/s at 60% load, my view is that
the 492Mb/s system is the better system. In the
long run the more efficient systems are the ones
that perform better generally.


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