DragonFly kernel List (threaded) for 2007-06
Re: implemented features (Re: Decision time....)
Michel Talon wrote:
> Rahul Siddharthan wrote:
> > Where is the generalisation? I said "my own code", which is what I'm
> > interested in. But it also appears to be true of GSL (the GNU
> > scientific library), at least the parts that I'm interested in. I
> > don't think, even if my claim was made "generally", it would be at all
> > controversial. Floating-point performance is much better in 64-bit
> > mode, and there are twice as many general-purpose registers available.
> I can confirm what Rahul is saying, perhaps this is no suprise since we are
> both theoretical physicists. I see 64 bits machines being *twice* faster
> than 32 bits machines (same machine, one in 32 bits Linux, the other in
> 64 bits Linux) on my computations, and particularly in symbolic maths
> computations, e.g. running maple 32 bits and maple 64 bits, or floating
> points computations. With this experience, i don't give any credence to the
> computer people who pretend that there is no difference between the two
> modes, or that you need >4 Gigs memory to see the difference. Our machines
> have 2 Gigs and i see an enormous difference.
I'm not a theoretical physicist, but I can confirm what you
are saying. :-) On certain algorithms amd64 machines are
considerably faster than i386 machines. For example I have
written a small Sudoku solver which is significantly faster
when compiled and run on an amd64 machine. I also believe
that it's because of the greater number of CPU registers
available in "long mode" of amd64 processors. (The machine
in question only has 1 GB of RAM, and the Sudoku processes
have a virtual size of only a few MB even, so the 4GB limit
is completely irrelevant here.)
It is also a popular fallacy that you need > 4 GB of RAM to
be able to use the larger address space of a 64bit machine.
That's wrong. The virtual address space of a process is
limited by the width of a pointer (which is 32 bit in i386
mode and 64 bit in amd64 mode), not by the amount of RAM.
You can have processes that are 8 GB in size on a machine
with 2 GB of RAM. Only in 64bit mode, of course.
Having said that, I appreciate all the work that Matt and
the others are doing. But there's only a limited number
of things you can work on with a (relatively) small team,
compared to the other BSDs. Frankly, I'm astonished how
much has been achieved in DF. Matt has done a tremendous
amount of work.
I'm sure that DF will grow amd64 support sooner or later,
it's probably not very difficult but just requires a
certain amount of time and effort. In fact it would be
a pity if Matt wasted his time on it.
Just my 2 cents. :-)
PS: I would really love to help DF myself, but my spare
time is extremely limited since I left university and went
into the "real business life" ... And even worse since I
got married. :)
Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing
Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd
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