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<div class="moz-cite-prefix">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): <br>
<br>
<a href="http://cpubenchmark.net/high_end_cpus.html">http://cpubenchmark.net/high_end_cpus.html</a><br>
<br>
<br>
Best regards,<br>
<br>
Michael Sluydts<br>
<br>
Op 12/09/2013 15:43, Luis Ogando schreef:<br>
</div>
<blockquote
cite="mid:CANpt3si7X6T2A2yLs2cggXqNaZ3gdQ7eVKATrRRky_MDXarw1w@mail.gmail.com"
type="cite">
<div dir="ltr">Dear Prof. Blaha,
<div><br>
</div>
<div style=""> Thank you very much for the explanations. They
will be very useful !!</div>
<div style=""> All the best,</div>
<div style=""> Luis</div>
</div>
<div class="gmail_extra">
<br>
<br>
<div class="gmail_quote">2013/9/12 Peter Blaha <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:pblaha@theochem.tuwien.ac.at" target="_blank">pblaha@theochem.tuwien.ac.at</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
This depends a lot on what you want to do and how much money
you have.<br>
<br>
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<br>
/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.<br>
<br>
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".<br>
<br>
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
.....<br>
<br>
Our strategy:<br>
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.<br>
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).
<div class="im">
<br>
<br>
On 09/11/2013 06:31 PM, Luis Ogando wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">
Dear Prof. Blaha,<br>
<br>
Just for curiosity, what processor did you buy ?<br>
Is the Xeon family better than the i7 one for WIEN2k
calculations ?<br>
All the best,<br>
Luis<br>
<br>
<br>
2013/9/11 Peter Blaha <<a moz-do-not-send="true"
href="mailto:pblaha@theochem.tuwien.ac.at"
target="_blank">pblaha@theochem.tuwien.ac.at</a><br>
</div>
<mailto:<a moz-do-not-send="true"
href="mailto:pblaha@theochem.tuwien.ac.at"
target="_blank">pblaha@theochem.tuwien.ac.at</a>>>
<div class="im"><br>
<br>
I don't know what "latest" means. We use the latest
one installed on<br>
our supercomputers (4.1.1.036)<br>
<br>
I have not seen any significant change with mpi in
the last years.<br>
<br>
PS: I just got info that we have now a new ifort
available for<br>
download ...<br>
<br>
<br>
On 09/11/2013 05:00 PM, Laurence Marks wrote:<br>
<br>
Thanks.<br>
<br>
One thing I will add/ask concerning the
parallelization, the latest<br>
impi seems to be substantially better -- have
you tried it? I<br>
have not<br>
just noticed this with Wien2k, but I am told
that others have seen<br>
improvements in other codes.<br>
<br>
On Wed, Sep 11, 2013 at 9:42 AM, Peter Blaha<br>
<<a moz-do-not-send="true"
href="mailto:pblaha@theochem.tuwien.ac.at"
target="_blank">pblaha@theochem.tuwien.ac.at</a><br>
</div>
<div>
<div class="h5">
<mailto:<a moz-do-not-send="true"
href="mailto:pblaha@theochem.tuwien.ac.at"
target="_blank">pblaha@theochem.tuwien.ac.at</a>>>
wrote:<br>
<br>
Before buying a couple of new computers, I
was asking myself<br>
the same<br>
question and discussed this with some
people of our<br>
computing departments.<br>
<br>
The conclusions:<br>
a) potentially very good, but in practice
very questionable,<br>
because for<br>
most application you cannot get out the
real speed (10 times<br>
faster than<br>
an Intel I7). This is true, even for many
lapack/mkl<br>
subroutines where<br>
it "should" work better.<br>
They told me to "wait", until the mkl
becomes better<br>
(hopefully). I'm<br>
not too optimistic, when you see how badly
the<br>
mkl-parallelization of<br>
multicore machines is working (2 cores is
very good, but 4<br>
or more is<br>
already very bad).<br>
<br>
b) The nature of our problem (big
eigenvalue problem): A "fast<br>
processor" is useful only for large
problems --> large memory.<br>
You can buy Phi coprocessors now with
quite some large<br>
memory, but then<br>
they are terrible expensive (and 5
"normal" PCs are faster<br>
and cheaper)<br>
<br>
c) the hardware design has a VERY slow
communication between<br>
main-memory<br>
and Phi-memory. This makes also
parallelization over several<br>
PHI-nodes<br>
via mpi not really possible (if you need
any significant<br>
data transfer,<br>
like for an eigenvalue problem).<br>
<br>
Thus I did not buy it.<br>
<br>
However, if anybody has access and time to
try out WIEN2k on<br>
PHis, I'd<br>
would be very interested in getting
feedback. (Maybe these<br>
computer-people were not good enough ....)<br>
<br>
PS: I know from G.Kresse that they had
some time ago (maybe<br>
2 years ?)<br>
an expert from NVIDIA with them. After 2
weeks of porting<br>
VASP to these<br>
GPUs by this expert, VASP on the GPU was
"almost as fast" as<br>
on an Intel<br>
I7 processor.<br>
<br>
<br>
On 09/11/2013 04:16 PM, Laurence Marks
wrote:<br>
<br>
Anyone know if these will be viable
with Wien2k (mpi,<br>
i.e. large problems)?<br>
<br>
<br>
--<br>
<br>
P.Blaha<br>
</div>
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<br>
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