[Beowulf] Theoretical vs. Actual Performance

[Prentice Bisbal]

This is my source for those theoretical numbers:

http://dewaele.org/~robbe/thesis/writing/references/49747D_HPC_Processor_Comparison_v3_July2012.pdf

If those numbers are off, that makes my job a bit easier.  And it looks 
like you're right. In the text above the table, it does mention 2-socket 
servers, and then below the table in fine print, it states

"For AMD Opteron Processors, theoretical FLOPS = Core Count x Core 
Frequency x number of processors per server x 4."

Why can't the table just show single socket performance? Grrrr....

Regardless of bad marketing and graphics design, I'm still at at square 
one. My system has 2 sockets, and the best I've been able to do is get 
~115 GFLOPS. And that's one of the 'instaneous' values LINPACK spits out 
every few seconds. At the end of test, the actual GFLOPS  result is more 
like 77 GLOPS:

===========================================
T/V                N    NB     P     Q Time                 Gflops
--------------------------------------------------------------------------------
WR00L2L2       82775    40     4     8 4924.71              7.678e+01

This is a two socket system, so that's only 27% of theoretical max.

Prentice

On 02/22/2018 01:18 PM, Dmitri Chubarov wrote:
> Hi,
>
> not sure if the 282 GFLOPS number is correct.
>
> We have 16 Bulldozer/Interlagos cores at 2.2 GHz. Each pair of cores 
> forms a CMT module. The two cores in the module share an FPU with 2 
> 128-bit FMAC units.
>
> In terms of double precision FLOPS it should make
> 16 * 2.2GHz * 2 double precision scalars/SIMD register * 2 FLOPS / FMA 
> op = 140.8 GFLOPS
>
> It looks like 282 GFLOPS number is per a 2P node.
>
> Dima
>
> On 22 February 2018 at 21:37, Prentice Bisbal <pbisbal at pppl.gov 
> <mailto:pbisbal at pppl.gov>> wrote:
>
>     Beowulfers,
>
>     In your experience, how close does actual performance of your
>     processors match up to their theoretical performance? I'm
>     investigating a performances issue on some of my nodes. These are
>     older systems using AMD Opteron 6274 processors. I found
>     literature from AMD stating the theoretical performance of these
>     processors is 282 GFLOPS, and my LINPACK performance isn't coming
>     close to that (I get approximately ~33% of that).  The number I
>     often hear mentioned is actual performance should be ~85%. of
>     theoretical performance is that a realistic number your experience?
>
>     I don't want this to be a discussion of what could be wrong at
>     this point, we will get to that in future posts, I assure you!
>
>     -- 
>     Prentice
>
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