F 15. 64 bit versus 32 bit.
Bill Davidsen
davidsen at tmr.com
Wed May 25 11:58:54 UTC 2011
Chris Adams wrote:
> Once upon a time, Fernando Cassia<fcassia at gmail.com> said:
>> Well guess what? 64 bit code is bigger (bigger pointers) and thus
>> slower, because CPU cache is less effective, with bigger code.
>
> All other things being equal, that might be true. However, all other
> things are NOT equal; pointer size is not the only different between
> i686 and x86_64. The biggest gain is that x86_64 has a much larger
> register set, so a lot of things don't have to hit RAM at all (and are
> much faster).
>
Unfortunately that biggest gain only occurs if the program logic is such that
registers run out often. So the gain only happens in a small number of possible
cases, where the compiler would otherwise get a value from L1 cache.
At the moment the slight (for most people) performance gain vs. the increased
hassle finding applications seems to favor case by case decisions. Neither is
such a major benefit to indicate everyone should make the same choice.
--
Bill Davidsen <davidsen at tmr.com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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