Re: Itanium2@900MHz slower than alpha@666MHz ?

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> On Fri, 24 Oct 2003 18:41:11 +0200, Ionut Georgescu <george@physik.tu-cottbus.de> said:

  >>  There are a lot of numbers at fftw.org, but from a cursory look
  >> at it, it does seem like peak performance of a 900MHz Itanium 2
  >> is significantly better than peak performance of an 833MHz Alpha.

  Ionut> and I am using 500 to 667 MHz alphas :-)

So are the numbers you're getting consistent with what's posted at
fftw.org?

  >>  Oh, one thing I noticed: the folks at fftw.org used "ecc -O3"
  >> whereas you used "ecc -O2".  The main difference with -O3 is that
  >> it turns on data prefetching.  This can make a huge difference
  >> when dealing with relatively large data sets.

  Ionut> Not for me. The ratio is approx. the same with smaller data
  Ionut> sets, which definitely fit into the L3 cache.

The prefetching is unlikely to make a big difference for data-sets
that fit in the data-set (even the L3 is quite fast on McKinley).
For out-of-cache data sets, it can make a big difference though.

	--david