[ODE] ODE slow on itanium?

Thomas Yeh tomyeh at CS.UCLA.EDU
Wed Dec 6 08:48:23 MST 2006

Did you verify the results from the Intel compiler binary visually?

I had problems when I tried to use icc.


On Wed, 6 Dec 2006, Bill Sellers wrote:

> Well gcc is certainly part of the problem. I've just recompiled
> everything using Intel's own icc and icpc using the -fast flag and it
> is quicker but it is still pretty slow. It was 3 times slower than
> the Opteron with gcc, now its only twice as slow which is still
> pretty disappointing (to me, since my University has just invested in
> a great big multiprocessor cluster based on itanium chips). I've also
> tried adding the -ftz flag which flushes denormals to zero on i64
> systems (according to the icc man page anyway) but it makes almost no
> difference at all so it's not that in my case.
> Cheers
> Bill
> On 5 Dec 2006, at 21:57, Francois Beaune wrote:
>> one thing to keep in mind is that itanium needs heavy
>> assistance from the compiler. i don't know how good
>> is gcc for itanium, but i suspect it is largely inferior to
>> a native compiler for that processor.
>> do you have access to the intel compiler for itanium?
>> francois
>> ----- Original Message -----
>> From: "Andreas Fredriksson" <deplinenoise at gmail.com>
>> To: "Bill Sellers" <wis at mac.com>
>> Cc: "ode-list list" <ode at q12.org>
>> Sent: Monday, December 04, 2006 20:38
>> Subject: Re: [ODE] ODE slow on itanium?
>>> On 12/3/06, Bill Sellers <wis at mac.com> wrote:
>>>> Hi All,
>>>> I've just been doing some benchmarking of my simulation on various
>>>> processors and they all behave about as I expect except for a truly
>>>> dreadful showing on a recent 1.6GHz Itanium system. It's over 3
>>>> times
>>>> slower than an Opteron 252 which is hardly cutting edge anymore, and
>>>> over twice as slow as the Xeon 5160 in my MacPro. They are all
>>>> compiled with gcc using the standard "-O3 -ffastmath" options.
>>>> Anyone
>>>> got any idea what's wrong since I don't think the Itanium should be
>>>> this slow...
>>> Make sure you're not gettig denormals propagating through your
>>> simulation; from what I've heard they're very slow on Itanium.
>>> They're
>>> also very slow on AMD and Intel hardware, unless by chance the
>>> precision of the simulation is different enough that you're only
>>> seeing the problem on the Itanium box.
>>> Good luck,
>>> Andreas
>>> --
>>> My other car is a cons.
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