Re: Itanium2@900MHz slower than alpha@666MHz ?
>>>>> On Tue, 21 Oct 2003 01:57:47 +0200, Ionut Georgescu <firstname.lastname@example.org> said:
Ionut> Thanks, I'll forward the message to that list. Can't check for dmesg
Ionut> right now because I started some benchmarks from www.fftw.org and I
Ionut> don't want to 'disturb'. I mainly want to see if I can reproduce their
Sounds like a good course of action.
Ionut> However, this is well tested code and it's been running on
Ionut> the alpha for months. Had there been any FP error, it would
Ionut> have crashed on the spot.
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.
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.
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.