[Wien] Intel(R) Xeon Phi™ coprocessor
Luis Ogando
lcodacal at gmail.com
Thu Sep 12 16:06:42 CEST 2013
Thank you, Michael ! This will be useful too !
Nevertheless, we can not forget that, sometime ago, Prof.
Blahacommented that the "Cache Memory" is more important than the
"clock" for
WIEN2K (discarding extreme cases, of course).
All the best,
Luis
2013/9/12 Michael Sluydts <michael.sluydts at ugent.be>
> While I'm not sure how easily normal desktop benchmarks transfer to
> parallel processing through wien2k I usually look at the following
> benchmarks when comparing CPUs (and prices):
>
> http://cpubenchmark.net/high_end_cpus.html
>
>
> Best regards,
>
> Michael Sluydts
>
> Op 12/09/2013 15:43, Luis Ogando schreef:
>
> 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>>
>>>
>>>
>>> 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>> 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><%2B43-1-58801-165300>
>>> FAX: +43-1-58801-165982 <tel:%2B43-1-58801-165982><%2B43-1-58801-165982>
>>> Email: blaha at theochem.tuwien.ac.at
>>> <mailto:blaha at theochem.tuwien.ac.at> WWW:
>>> http://info.tuwien.ac.at/__theochem/
>>> <http://info.tuwien.ac.at/theochem/>
>>>
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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><%2B43-1-58801-165300>
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>>> Email: blaha at theochem.tuwien.ac.at
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>>> http://info.tuwien.ac.at/__theochem/
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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/theochem/
>> --------------------------------------------------------------------------
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