Date: Tue, 13 Apr 2010 00:30:09 -0500 From: Alan Cox <alan.l.cox@gmail.com> To: Maho NAKATA <chat95@mac.com> Cc: freebsd-stable@freebsd.org Subject: Re: Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920 Message-ID: <h2yca3526251004122230l909bc93ey916d7fe0dd24fd33@mail.gmail.com> In-Reply-To: <20100412.131213.4959786962516027.chat95@mac.com> References: <20100412.131213.4959786962516027.chat95@mac.com>
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On Sun, Apr 11, 2010 at 11:12 PM, Maho NAKATA <chat95@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 These statements about FreeBSD's memory management are wrong, or at least outdated.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
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