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

On Mon, Oct 20, 2003 at 05:22:19PM -0700, David Mosberger wrote:
> I wasn't very clear: fpswa stands for "floating-point software assist"
> which is a trap that gets invoked when encountering a corner-case that
> isn't handled in hardware (such as operations on infinity, NaN, or
> denormals).  The traps are handled in the kernel and do _not_ result
> in an error, but such operatiosn of course to run more slowly.  Alpha
> behaves very similar, so like I mentioned earlier, it's unlikely to be
> an issue with fftw2.

This is not an issue: dmesg doesn't show anything like this and the
program would crash on the alpha if it were.

> 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.

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

> 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.

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


* Ionut Georgescu
* http://www.physik.tu-cottbus.de/~george/
* Registered Linux User #244479
* "In Windows you can do everything Microsoft wants you to do; in Unix you
*                can do anything the computer is able to do."

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