[Wien] Intel(R) Xeon Phi™ coprocessor

[Peter Blaha]

Before buying a couple of new computers, I was asking myself the same 
question and discussed this with some people of our computing departments.

The conclusions:
a) potentially very good, but in practice very questionable, because for
most application you cannot get out the real speed (10 times faster than 
an Intel I7). This is true, even for many lapack/mkl subroutines where 
it "should" work better.
They told me to "wait", until the mkl becomes better (hopefully). I'm 
not too optimistic, when you see how badly the mkl-parallelization of 
multicore machines is working (2 cores is very good, but 4 or more is 
already very bad).

b) The nature of our problem (big eigenvalue problem): A "fast 
processor" is useful only for large problems --> large memory.
You can buy Phi coprocessors now with quite some large memory, but then 
they are terrible expensive (and 5 "normal" PCs are faster and cheaper)

c) the hardware design has a VERY slow communication between main-memory 
and Phi-memory. This makes also parallelization over several PHI-nodes 
via mpi not really possible (if you need any significant data transfer, 
like for an eigenvalue problem).

Thus I did not buy it.

However, if anybody has access and time to try out WIEN2k on PHis, I'd 
would be very interested in getting feedback. (Maybe these 
computer-people were not good enough ....)

PS: I know from G.Kresse that they had some time ago (maybe 2 years ?) 
an expert from NVIDIA with them. After 2 weeks of porting VASP to these 
GPUs by this expert, VASP on the GPU was "almost as fast" as on an Intel 
I7 processor.


On 09/11/2013 04:16 PM, Laurence Marks wrote:
> Anyone know if these will be viable with Wien2k (mpi, i.e. large problems)?
>

-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WWW: 
http://info.tuwien.ac.at/theochem/
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