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 <[email protected]
<mailto:[email protected]>>
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
<[email protected]
<mailto:[email protected]>> 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
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FAX: +43-1-58801-165982 <tel:%2B43-1-58801-165982>
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------------------------------__------------------------------__--------------
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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