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
