F 15. 64 bit versus 32 bit.

[Jerry Feldman]

On 05/24/2011 12:37 PM, Fernando Cassia wrote:
> Well guess what? 64 bit code is bigger (bigger pointers) and thus
> slower, because CPU cache is less effective, with bigger code.
>
In my previous job I've done quite a bit of benchmarking. First, the OS
itself is faster in 64-bit because it can use the additional GP
registers, and memory access is linear. I've seen many cases where
32-bit apps run faster than 64-bit apps, but I have also seen cases
where 32-bit apps run faster using a 64-bit OS than they do with the
same 32-bit OS. I have not tested Java, where the article you reference
(http://su.pr/23Ic43) is strictly a Java article. While I was at Digital
in the 90s, the Alpha was a pure 64-bit platform, and we came up with
some ways to allow 32-bit applications to be built and run under Tru64.
But, most of my benchmark testing on both x86 and IA64 points the fact
that most 64-bit apps will be faster or not suffer any performance
degradation. The bottom line here is you can't make a blanket statement
that 64-bit code is slower. And if you have a decent optimizing
compiler, your performance could improve.


-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846


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