dd test discussion (was Re: possible regression?)

[Henry Gebhardt]

On Sat, Jan 22, 2011 at 11:49:43AM +0700, Mulyadi Santosa wrote:
> On Fri, Jan 21, 2011 at 20:25, Mag Gam <magawake at gmail.com> wrote:
> > Anyone had a chance to try this? :-)
> 
> $ for a in `seq 1 3`; do \time dd bs=4K count=1M if=/dev/zero of=/dev/null; done

Hm, I also wrote a little script to go through more values of bs.  The
script is attached.  To change what values to use for bs, change the
variables $min, $step, and $max at the beginning of the script, which
are the parameters for "seq".  To get a graph of throughput versus bs,
use it like so:

   $ ./pipespeed.sh > data
   [...]
   $ gnuplot
   plot "data" w l

The highest I get is 8.5 GB/s with bs=22528 on 2.6.37.

How can you get a speed of 30 GB/s?  It seems excessively fast. :)


Greetings,

Henry
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