[Llvm-bgq-discuss] Performance relative to Xeons

[Jack Poulson]

Hello,

I have benchmarking my code on Vesta and, while I have been seeing
excellent strong scaling, I am a little underwhelmed by the wall-clock
timings relative to my desktop (Intel(R) Xeon(R) CPU E5-1603 0 @ 2.80GHz).
I am using the newest version of bgclang++ on Vesta, and g++-4.7.2 on my
desktop (both used -O3), and I am seeing roughly a factor of four
difference in performance on the same number of cores.

If I ignored the fact that I am using a vendor math library on BGQ and
reference implementations on my desktop, I would expect the BGQ timings to
be a factor of 1.75 slower due to clockspeed differences. Would anyone have
an explanation for the additional factor of more than 2x? My algorithm
spends most of its time in sin/cos/sqrt evaluations and dgemm with two
right-hand sides.

Thanks,
Jack
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