[Llvm-bgq-discuss] Performance relative to Xeons

[Hal Finkel]

----- Original Message -----
> From: "Jack Poulson" <jack.poulson at gmail.com>
> To: llvm-bgq-discuss at lists.alcf.anl.gov
> Sent: Tuesday, March 5, 2013 12:59:06 PM
> Subject: [Llvm-bgq-discuss] Performance relative to Xeons
> 
> 
> 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.

How many threads per core are you using? Can you please link with the HPM library and let me look at the performance summary files?

> 
> 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.

You're linking to libmass for the special functions, right? [on my TODO list is to do this automatically in fast-math mode, but I've not implemented this yet].

> 
> Thanks,
> Jack
> 
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