[Beowulf] Theoretical vs. Actual Performance

[Joe Landman]

On 02/22/2018 09:37 AM, Prentice Bisbal 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?

85% makes the assumption that you have the systems configured in an 
optimal manner, that the compiler doesn't do anything wonky, and that, 
to some degree, you isolate the OS portion of the workload off of most 
of the cores to reduce jitter.   Among other things.

At Scalable, I'd regularly hit 60-90 % of theoretical max computing 
performance, with progressively more heroic tuning.   Storage, I'd 
typically hit 90-95% of theoretical max (good architectures almost 
always beat bad ones).  Networking, fairly similar, though tuning per 
use case mattered significantly.

>
> 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!
>

-- 
Joe Landman
t: @hpcjoe
w: https://scalability.org