[Beowulf] [External] Re: HPCG benchmark, again

[Prentice Bisbal]

M,

Isn't it more accurate to say that HPCG measures the whole system more 
realistically, and memory bandwidth happens to be the "rate limiting 
step" in just about all architectures? Even with LINPACK, which should 
be CPU-bound, the Top500 list shows that HPL results are affected by the 
network. For example, there's this article which is a bit old, but I 
think still applies (doing the same analysis on the current top500 list 
is on my to-do list, actually):

https://www.nextplatform.com/2015/07/20/ethernet-will-have-to-work-harder-to-win-hpc/

On 3/18/22 8:34 PM, Massimiliano Fatica wrote:
> HPCG measures memory bandwidth, the FLOPS capability of the chip is 
> completely irrelevant.
> Pretty much all the vendor implementations reach very similar 
> efficiency if you compare them to the available memory bandwidth.
> There is some effect of the network at scale, but you need to have a 
> really large  system to see it in play.
>
> M
>
> On Fri, Mar 18, 2022 at 5:20 PM Brian Dobbins <bdobbins at gmail.com> wrote:
>
>
>     Hi Jorg,
>
>       We (NCAR - weather/climate applications) tend to find that HPCG
>     more closely tracks the performance we see from hardware than
>     Linpack, so it definitely is of interest and watched, but our
>     procurements tend to use actual code that vendors run as part of
>     the process, so we don't 'just' use published HPCG numbers. 
>     Still, I'd say it's still very much a useful number, though.
>
>       As one example, while I haven't seen HPCG numbers for the MI250x
>     accelerators, Prof. Matuoka of RIKEN tweeted back in November that
>     he anticipated that to score around 0.4% of peak on HPCG, vs 2% on
>     the NVIDIA A100 (while the A64FX they use hits an impressive 3%):
>     https://twitter.com/ProfMatsuoka/status/1458159517590384640
>
>       Why is that relevant?  Well, /on paper/, the MI250X has ~96 TF
>     FP64 w/ Matrix operations, vs 19.5 TF on the A100.  So, 5x in
>     theory, but Prof Matsuoka anticipated a ~5x differential in HPCG,
>     /erasing/ that differential.  Now, surely /someone/ has HPCG
>     numbers on the MI250X, but I've not yet seen any.  Would love to
>     know what they are.  But absent that information I tend to bet
>     Matsuoka isn't far off the mark.
>
>       Ultimately, it may help knowing more about what kind of
>     applications you run - for memory bound CFD-like codes, HPCG tends
>     to be pretty representative.
>
>       Maybe it's time to update the saying that 'numbers never lie' to
>     something more accurate - 'numbers never lie, but they also rarely
>     tell the whole story'.
>
>       Cheers,
>       - Brian
>
>
>     On Fri, Mar 18, 2022 at 5:08 PM Jörg Saßmannshausen
>     <sassy-work at sassy.formativ.net> wrote:
>
>         Dear all,
>
>         further the emails back in 2020 around the HPCG benchmark
>         test, as we are in
>         the process of getting a new cluster I was wondering if
>         somebody else in the
>         meantime has used that test to benchmark the particular
>         performance of the
>         cluster.
>         From what I can see, the latest HPCG version is 3.1 from
>         August 2019. I also
>         have noticed that their website has a link to download a
>         version which
>         includes the latest A100 GPUs from nVidia.
>         https://www.hpcg-benchmark.org/software/view.html?id=280
>
>         What I was wondering is: has anybody else apart from Prentice
>         tried that test
>         and is it somehow useful, or does it just give you another set
>         of numbers?
>
>         Our new cluster will not be at the same league as the
>         supercomputers, but we
>         would like to have at least some kind of handle so we can
>         compare the various
>         offers from vendors. My hunch is the benchmark will somehow
>         (strongly?) depend
>         on how it is tuned. As my former colleague used to say: I am
>         looking for some
>         war stories (not very apt to say these days!).
>
>         Either way, I hope you are all well given the strange new
>         world we are living
>         in right now.
>
>         All the best from a spring like dark London
>
>         Jörg
>
>
>
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