[svlug] Maximum memory (debian 3.1)

[Greg Lindahl]

On Wed, Mar 21, 2007 at 02:44:08PM -0700, Edward Cherlin wrote:
> > Neither of the examples I gave will improve. Our compiler is used to
> > build itself, and we're a much better 64-bit compiler than 32-bit
> > compiler (in 64 bit mode, we're #1 on Opteron, and tied with Intel for
> > floating point on Woodcrest), but it uses a lot of pointers, and
> > making them twice as large is a big loss.
> 
> How big a loss, vs. how much gain in performance? Even without seeing
> the numbers, I'm sure that I would take the hit on memory for any
> system that I would actually use for compute-intensive work. At
> $100/G, what's the issue?

The general performance gain for 64 bit x86 is 10-15% over 32-bit
(more registers, better calling convention).

The performance loss on our code for bigger pointers is ~ 50% (worse
cache behavior.)

As for buying more memory, our customers don't like doing that just
for compilation. They'll buy more memory for their apps, but the
compiler is supposed to give correct, fast code while taking no time
to compile & have small memory usage. (sarcasm alert.)

-- greg