[Beowulf] itanium vs. x86-64
toon.knapen at gmail.com
Mon Feb 9 23:42:38 PST 2009
Mark Hahn wrote:
>> I have been working on itanium machines for a year now and I actually
>> the hw pretty elegant and the dev software stack on top of it (compiler,
>> profiler etc) pretty handy.
> aren't all the same tools available on x86_64? or were you referring
> to, eg,
> something SGI-specific?
Actually I'm using an itanium in an HP-integrity server. The tools I'm
referring to are the HP C and C++ compiler and their profiler called
The C compiler for instance can add memory-debugging code (do not know
any compiler with a similar feature, valgrind nevertheless is more
powerfull). Next caliper allows to get a lot of diagnostics from the cpu
(also because ia64 supports all that while x86-64 does not AFAICT) like
number of bubbles in the pipeline, L2-cache misses, clock-cycles per
line of C-code etc.
>> but now with the Tukwila switching to the QuickPath, how do you guys
>> Itanium will perform in comparison to Xeon's and Opteron's ?
> this change would be interesting if it meant that the next-gen numalink
> box could take nehalems rather than ia64. I can't really understand why
> Intel has stuck with ia64 this long - perhaps the economy will provide
> the fig-leaf necessary to dump it.
Are you sure nehalem will outperform ia64. I will probably switch from
ia64 to x86-64 and knowing that my code is mostly memory-bound, I'm
wondering what I will gain. Of course the only way to know is to test
it but that has not been possible yet.
> (why am I down on ia64? mainly the sense of unfulfilled promise: the
> ISA was
> supposed to provide some real advantage, and afaikt never has. the VLIW-ie
> ISA was intended to avoid clock scaling problems created by CISC decode and
> OOO, no? but the ia64 seems to have only distinguished itself by
> large caches and offering cache-coherency hooks to SGI. have other
> people had the experience ia64 doing OK on code with
> regular/unrollable/prefetchable data patterns, but poorly otherwise?)
I'm not able to compare yet because I have not run the code on anything
else than ia64. But caliper allowed me to get a lot of diagnostics on
the cpu while running my code that allowed me to optimise easily.
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