64-bit Kernel Question

[Tom Lane]

"Patrick O'Callaghan" <pocallaghan at gmail.com> writes:
> On Mon, 2009-03-09 at 12:49 -0700, Adam Williamson wrote:
>> The most common CPU-bound operation in our world, I guess, is
>> compilation, and you would notice a definite improvement in speed there,
>> running x86-64 vs x86-32 - not huge, but noticeable. Certain database
>> and I think scientific operations that are CPU-bound also derive a
>> significant benefit. It depends on whether the code can take advantage
>> of much bigger registers, AIUI.

> Anyone who does even casual video processing (e.g. with transcode
> filters) definitely will notice. This is something that pegs both cores
> to 100% when I run it, until the fan kicks in and it slows a bit.

It's not so much about *bigger* registers as *more* registers.  The
x86 architecture is incredibly register-starved (what comes of being
bug-compatible with a 1971 CPU design...).  When AMD did the x86_64
redesign they took advantage of the opportunity to define a more
reasonable number of registers.  Avoiding swapping values in and out
to memory all the time is a large chunk of the reason for the
performance boost in x86_64 code.  It's not uncommon for x86_64
code to be physically smaller than comparable x86 code because of
elimination of those extra instructions, even though the individual
instructions tend to be wider.

But I agree that a lot of people seldom do anything CPU-intensive
enough to notice.

			regards, tom lane