[Pw_forum] Re: Woodcrest vs Opteron performance in pwscf calc.

[Huiqun Zhou]

Kostya and list-users,

Thanks for your comment and recommendation. Considering the 
price/performance
of machines with dempsey and woodcrest, dempsey may be a good choice too,
especially if you have no problem to pay the electricity bill ;-)

You mentioned NUMA enabling on opteron machines, I wonder if it's a default
function of kernel 2.6.9-xx. If it's not, I need to turn it on in 
re-configuration of
the kernel and recompile, right?

Thanks,

Huiqun

----- Original Message ----- 
From: "Konstantin Kudin" <konstantin_kudin at yahoo.com>
To: <pw_forum at pwscf.org>
Sent: Tuesday, August 08, 2006 12:00 AM
Subject: Re: [Pw_forum] Re: Woodcrest vs Opteron performance in pwscf calc.


>
> Dempsey and Opterons do 2 BLAS operations per cycle, while Woodcrest
> does 4. So effectively you get these frequencies for BLAS (per core):
> Woodcrest (4x2.66=10.6), Dempsey (3.2x2=6.4), Opteron ( 2.6x2=5.2).
> That is exactly the order you get in terms of performance. Your Opteron
> scaling is not too good, which either suggests that there is not enough
> memory bandwidth, or you do not have NUMA turned on.
>
> Now, the theoretical performance would translate into the real world
> if the memory is fast enough. I think both Dempsey and Woodcrest use
> the same chipset with 2 buses, so earlier memory contention issues with
> multiple Intel chips are mostly gone for now. Still, you see that with
> 4 Woodcrest cores the speedups are worse then for Dempsey, which
> suggests that perhaps the optimal purchase for QE would be lower
> frequency chips, such as 2.0 or 2.33 Ghz since 4 2.66 Ghz cores are too
> fast for the memory.
>
> Kostya
>