AMD Athlon64 Systems

[Mike A. Harris]

On Sat, 18 Oct 2003, Chris Ricker wrote:

>In general, it's always going to be true that 32-bit userspace is better
>than 64-bit userspace for apps that don't need to be 64-bit, simply because
>you'll avoid as much cache thrashing and such.

On processors like sparc, ppc, sure.

>Isn't the reason that's not true with 64-bit vs 32-bit on AMD64
>is because in 32-bit, AMD64 is quite register-starved, and the
>gains from additional registers in 64-bit more than offset the
>losses from memory bloat?

Exactly, plus the fact that AMD64 has a lot more onchip CPU cache 
memory right out of the floodgates, which minimizes/eliminates 
losses for the most part.

Really though, one only needs to pick a couple of different 
applications, and compare running 32bit vs. 64bit versions under 
the same kernel.  I've done a limited amount of benching, but 
haven't kept the numbers.  It's easy enough for people with the 
hardware to whip up some simple tests though.




-- 
Mike A. Harris     ftp://people.redhat.com/mharris
OS Systems Engineer - XFree86 maintainer - Red Hat