avgtime - Small D util for your everyday benchmarking needs

Juan Manuel Cabo juanmanuel.cabo at gmail.com
Fri Mar 23 01:02:01 PDT 2012


On Friday, 23 March 2012 at 05:16:20 UTC, Andrei Alexandrescu 
wrote:
[.....]
>> (man, the gaussian curve is everywhere, it never ceases to
>> perplex me).
>
> I'm actually surprised. I'm working on benchmarking lately and 
> the distributions I get are very concentrated around the 
> minimum.
>
> Andrei


Well, the shape of the curve depends a lot on
how the random noise gets inside the measurement.

I like  'ls -lR'  because the randomness comes
from everywhere, and its quite bell shaped.
I guess there is a lot of I/O mess (even if
I/O is all cached, there are lots of opportunities
for kernel mutexes to mess everything I guess).

When testing "/bin/sleep 0.5", it will be quite
a pretty boring histogram.

And I guess than when testing something thats only
CPU bound and doesn't make too much syscalls,
the shape is more concentrated in a few values.


On the other hand, I'm getting some weird bimodal
(two peaks) curves sometimes, like the one I put on
the README.md.
It's definitely because of my laptop's CPU throttling,
because it went away when I disabled it (for the curious
ones, in ubuntu 64bit, here is a way to disable
throttling (WARNING: might get hot until you undo or reboot):

echo 1600000 > 
/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq

echo 1600000 > 
/sys/devices/system/cpu/cpu1/cpufreq/scaling_min_freq

(yes my cpu is 1.6GHz, but it rocks).


--jm





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