[Beowulf] quad-core SPECfp2006: where are 4 FPresults/cycle ?
kus at free.net
Sat Oct 13 07:57:05 PDT 2007
In message from Mark Hahn <hahn at mcmaster.ca> (Fri, 12 Oct 2007
16:09:05 -0400 (EDT)):
>> This means that 2 additional FP results per cycle in
>> only about 7% of performance increase :-(
>the 4 flops/cycle is really for linpack-like code: it assumes you are
>executing packed double SIMD.
Yes, but AFAIK most of the modern optimizing F9x compilers for x86 can
generate codes w/SSEx instructions (instead of x87). And I assume that
many real world codes, including some from SPECfp2006 set, includes
the work w/floating point vectors. It's not necessary to have very
long vectors - taking into account that 64 bit SSE vectors have
Such things may gives theoretically 2x speedup !
>just that not all FP is SIMD-friendly, I think.
Yes, I agree w/"not all". But 7% speedup means, I beleive, "very
seldom FP codes" ?
> if your code spends
>a lot of time in blas/lapack functions, I would expect it to see good
>regards, mark hahn.
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