[Beowulf] Q: AMD Opteron (Barcelona) 2356 vs Intel Xeon 5460

Vincent Diepeveen diep at xs4all.nl
Wed Sep 17 17:27:37 EDT 2008


Nah,

I guess he's referring to sometimes it's using single precision  
floating point
to get something done instead of double precision, and it tends to keep
sometimes stuff in registers.

That isn't a problem necessarily, but if i remember well floating  
point state
could get wiped out when switching to SSE2.

Sometimes you lose your FPU registerset in that case.

Main problem is that there is so many dangerous optimizations possible,
to speedup testsets, because in itself floating point is real slow to  
do at hardware,
from hardware viewpoint seen.

Yet in general last generations of intel compilers that has improved  
really a lot.



Vincent

On Sep 17, 2008, at 10:25 PM, Greg Lindahl wrote:

> On Wed, Sep 17, 2008 at 03:43:36PM -0400, Eric Thibodeau wrote:
>
>> Also, note that I've had issues with icc
>> generating really fast but inaccurate code (fp model is not IEEE *by
>> default*, I am sure _everyone_ knows this and I am stating the  
>> obvious
>> here).
>
> All modern, high-performance compilers default that way. It's  
> certainly
> the case that sometimes it goes more horribly wrong than necessary,  
> but
> I wouldn't ding icc for this default. Compare results with IEEE mode.
>
> -- greg
>
>
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