Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920

[Alan Cox]

On Sun, Apr 11, 2010 at 11:12 PM, Maho NAKATA <chat95 at mac.com> wrote:

> Hi FreeBSD developers,
> [the original article in Japanese can be found at
> http://blog.goo.ne.jp/nakatamaho/e/b5f6fbc3cc6e1ac4947463eb1ca4eb0a ]
>
> *Abstract*
> I compared the peak performance of FreeBSD 8.0/amd64 and Ubuntu 9.10 amd64
> using dgemm
> (a linear algebra routine, matrix-matrix multiplication).
> I obtained only 70% of theoretical peak performance on FreeBSD 8/amd64 and
> almost 95% on Ubuntu 9.10 /amd64. I'm really disappointed.
>
> *Introduction*
> I'm a friend of Gotoh Kazushige, the principal developers of GotoBLAS. He
> told me that
> FreeBSD is not suitable OS for scientific computing or high performance
> computing. He says
> (in Japanese and my translation):
>
> > I guess FreeBSD does page coloring, but I don't think FreeBSD considers
> very large cache
> > size which recent CPU has. Support of a very large cache on Linux is
> still not very will
> > sophisticated, but on *BSDs, its worst; they uses too fine memory
> allocation method,
> > so we cannot expect large continuous physical memory allocation.
>

These statements about FreeBSD's memory management are wrong, or at least
outdated.  FreeBSD is very likely to allocate physical memory in contiguous
chunks to your memory-hungry application even if automatic superpage
promotion does not occur.

You should refer your friend to my paper at
http://www.usenix.org/events/osdi02/tech/full_papers/navarro/navarro_html/and
tell him that FreeBSD >= 7.2 implements a variation on what that paper
describes.

Regards,
Alan