memory alignment and blas

[Paul Kienzle]

I was playing a bit with memory alignment to see what
effect it would have on the performance of DGEMM.

For pentium II, I didn't see any performance effect.
This is with Debian and atlas3-base installed.

For PPC G4, unaligned memory shows 7.5x worse
performance than aligned memory.  4 byte aligned
memory shows < 10% performance drop.  8 byte
alignment is indistinguishable from 128 byte alignment.

As far as I can tell, the OS X allocator returns 8 byte
aligned memory, so no special effort is required
to support it.

My octave version is too out of date on MIPS to give
any performance numbers.

I'm attaching the code I used to test this.

Paul Kienzle
address@hidden

align.cc
Description: Binary data