[Wien] Intel(R) Xeon Phi™ coprocessor
Luis Ogando
lcodacal at gmail.com
Thu Sep 12 15:43:54 CEST 2013
Dear Prof. Blaha,
Thank you very much for the explanations. They will be very useful !!
All the best,
Luis
2013/9/12 Peter Blaha <pblaha at theochem.tuwien.ac.at>
> This depends a lot on what you want to do and how much money you have.
>
> The single-core speed of a fast I7 is at least as good (or faster) than
> most Xeons, and they are MUCH cheaper. So for all systems up to 64-100
> atoms/cell, where you need several k-points, a small cluster of I7 cpus
> /4 cores, or more expensive 6 core) (with GB-network and a common NFS file
> system) is for sure the fastest platform and in particular has by FAR the
> best price/performance ratio (One powerful I7 computer may cost about 1000
> Euro). For bigger clusters, a drawback can be the large "space" to put all
> PCs on a big shelf ....), but if you have less than 10000 Euros, this is
> probably the best choice.
>
> However, Xeons can be coupled (2-4 Xeons) to a "single multicore computer
> (eg. 16 cores)", which may work with mpi and can be used to handle systems
> up to 200-300 atoms. They also can be bought in small boxes and may fit in
> a single 19 inch cabinet. But of course such systems are much more
> expensive. From what I said above it should be clear, that it is completely
> useless to buy a "single 4 core Xeon computer".
>
> The next step would be to buy an Infiniband switch+cards and couple your
> PCs with this fast network to a powerful multinode mpi-cluster. Since the
> switch/cards are fairly expensive, on usually takes here Xeons as platform.
> However, you need to know how to install/configure the software properly.
> I've seen such clusters even in computing centers, which were completely
> useless, because the network/mpi was instable and jobs would crash randomly
> every couple of hours .....
>
> Our strategy:
> i) We have a GB-networked cluster with Intel I7 computers (which we
> maintain our-self and this cluster includes also all the user-
> workstations) and do all the calculations for systems up to 64 atoms/cell
> on these systems.
> 2) For bigger systems we go to our University computer-center and run
> there with a PBS queuing system. This has the advantage that we do not need
> to care about the installation of the infiniband network nor the
> mpi-infrastructure (but we use always intel-mpi together with ifort/mkl).
>
>
> On 09/11/2013 06:31 PM, Luis Ogando wrote:
>
>> Dear Prof. Blaha,
>>
>> Just for curiosity, what processor did you buy ?
>> Is the Xeon family better than the i7 one for WIEN2k calculations ?
>> All the best,
>> Luis
>>
>>
>> 2013/9/11 Peter Blaha <pblaha at theochem.tuwien.ac.at
>> <mailto:pblaha at theochem.**tuwien.ac.at <pblaha at theochem.tuwien.ac.at>>>
>>
>>
>> I don't know what "latest" means. We use the latest one installed on
>> our supercomputers (4.1.1.036)
>>
>> I have not seen any significant change with mpi in the last years.
>>
>> PS: I just got info that we have now a new ifort available for
>> download ...
>>
>>
>> On 09/11/2013 05:00 PM, Laurence Marks wrote:
>>
>> Thanks.
>>
>> One thing I will add/ask concerning the parallelization, the
>> latest
>> impi seems to be substantially better -- have you tried it? I
>> have not
>> just noticed this with Wien2k, but I am told that others have seen
>> improvements in other codes.
>>
>> On Wed, Sep 11, 2013 at 9:42 AM, Peter Blaha
>> <pblaha at theochem.tuwien.ac.at
>> <mailto:pblaha at theochem.**tuwien.ac.at<pblaha at theochem.tuwien.ac.at>>>
>> wrote:
>>
>> 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
>> ------------------------------**
>> __----------------------------**--__--------------
>>
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060
>> Vienna
>> Phone: +43-1-58801-165300 <tel:%2B43-1-58801-165300>
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>> --
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>> P.Blaha
>> ------------------------------**__----------------------------**
>> --__--------------
>>
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>> Phone: +43-1-58801-165300 <tel:%2B43-1-58801-165300>
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> --
>
> P.Blaha
> ------------------------------**------------------------------**
> --------------
> 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/**
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