Why my cp2k.popt is running much slower than cp2k.sopt?

Axel akoh... at gmail.com
Thu Jul 24 23:22:34 CEST 2008

> It seems that the MPI performace is really bad. It spent a lot of time
> in calling MP_Allreduce and MP_Wait. For cp2k.sopt it took only 162

right this is what is needed. a lot. and this is why cp2k needs
a very fast and low latency network and a good MPI implementation.

> seconds to finish the job while it took 3010 seconds to finish the
> same job. There must be something wrong the executable cp2k.popt since
> my other parallel executable can be run using the same /home/mpich.g95/
> bin/mpirun with normal performance.  Any suggestions?

before discussing any cp2k related issues. you should first
check how well your MPI setup works _at all_. i suspect there
is a much lower lying problem than cp2k and its requirements.

most MPI packages come with some benchmark examples to measure
performance and latencies. i suggest to try those first and
check how well your setup works and compare it to similar
set ups. it would help a _lot_ if you give a sufficiently detailed
account of your hardware when discussing performance. please
see earlier discussions on the subject.

if collective operations and barriers are giving you problems
than your may not be using your machine correctly or have not
set it up correctly. they should also matter a lot in case of
using TCP/IP connections for parallel computation which incur
large latency penalties due to the TCP/IP encoding. the fact
that you are using MPICH doesn't help as well, since its
collectives, especially in version 1.x.x, are supposed to be
pretty inefficient.

what is worrying me even more is the fact that you seem to be
running your tests as root. this goes against about everything
i've learned during my carreer about good computer use practices.

basically the root account should only used if it cannot be avoided.
to give an example: on our own local clusters (where i do maintain
MPI, compilers, libraries and most applications including cp2k)
i don't even _know_ the root password (and don't _want_ to, since
this way, it is close to impossible to mess up the machines by
accident or carelessness).


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