[Pw_forum] a strange behavior for QE-v4 compared with QE-v3

[lan haiping]

Hi, Schmidt, i will try your method to build QE for other
machines.  thanks for your sharing.
best
On Wed, Nov 26, 2008 at 10:52 PM, JR Schmidt <schmidt at chem.wisc.edu> wrote:

> I ran into this same issue.  Let me say that (for whatever reason)
> setting OMP_NUM_THREADS, or MKL_NUM_THREADS did not seem to fix the
> problem.  MKL was still creating many threads per process, though
> perhaps only one thread was active at at time.
>
> I found a better solution, offering increased performance at least for
> parallel jobs, was to link with the MKL serial library.  This can be
> done by modifying the following lines in make.sys (for MKL 10)
>
> BLAS_LIBS =  -lmkl_intel_lp64 -lmkl_sequential -lmkl_core
> LAPACK_LIBS =  -lmkl_intel_lp64 -lmkl_sequential -lmkl_core
>
> then doing:
> make clean (probably unnecessary)
> make
>
> Although this gives WORSE performance when you are only running a single
> job (since it does not thread to take advantage of the other cores), if
> you are trying to fully utilize your nodes by running several jobs or
> parallel jobs, using the threaded library results in a giant mess.
>
> > this looks a lot like you are using two different versions
> > of MKL for the two compiles and thus are another "victim"
> > of the automatic threading of MKL v10. you should not
> > have a process with >100% CPU with a regular compile.
> > now if you have 8 cores and 8 MPI tasks and each of them
> > threads across 8 cores, you have a) a severe overload of
> > the scheduler and b) a big mess and all kinds of bad
> > performance issues.
> >
> > try setting OMP_NUM_THREADS=1 and check if that
> > changes the behavior.
> >
> --
> J.R. Schmidt
> Assistant Professor of Chemistry
> Room 8305D
> Department of Chemistry
> University of Wisconsin-Madison
> 1101 University Ave
> Madison, WI 53706
>
> Phone: (608) 262-2996
> Fax: (608) 262-9918
> E-mail: schmidt at chem.wisc.edu
> http://www.chem.wisc.edu/people/profiles/schmidt.php
>
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-- 
Hai-Ping Lan
Department of Electronics ,
Peking University , Bejing, 100871
lanhaiping at gmail.com, hplan at pku.edu.cn
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