[Wien] OMP_NUM_THREADS

[Dr Qiwen YAO]

Dear Gerhard,
Thank you very much for your respond.
I am a bit slow in catching up with what you are saying, may I rephrase what you've suggested and see is I could understand what you are suggesting:

For 4 k-points and 4 mkl thread - do you mean I would set 4 lines of "1:localhost" in the .machines file and set OMP_NUM_THREADS=4?

And for the 2 k points and 2 mkl threads - do I set only 2 lines of  "1:localhost" in the .machines file and set OMP_NUM_THREADS=2?

If I am understanding you correctly, I will try both scenario and see which one is more efficient.
 
Thank you so much for your time and help!

Qiwen


------Original Message------
From:"Gerhard Fecher"<fecher at uni-mainz.de>
To:"A Mailing list for WIEN2k users"<wien at zeus.theochem.tuwien.ac.at>
Cc:
Subject:Re: [Wien] OMP_NUM_THREADS
Date:07/27/2011 03:17:21 PM(+0000)
>If you have four "real" cores you may run in parallel either 4 k-points or 4 mkl threads or 2 k points and 2 mkl threads
>
>In some cases it might be good to "switch off the virtual cores" in the bios, at least with older processors/compilers this was faster,
>but I did not check anymore.
>
>Ciao
>Gerhard
>
>====================================
>Dr. Gerhard H. Fecher
>Institut of Inorganic and Analytical Chemistry
>Johannes Gutenberg - University
>55099 Mainz
>________________________________________
>Von: wien-bounces at zeus.theochem.tuwien.ac.at [wien-bounces at zeus.theochem.tuwien.ac.at]&quot; im Auftrag von &quot;Dr Qiwen  YAO [Yao.Qiwen at nims.go.jp]
>Gesendet: Mittwoch, 27. Juli 2011 14:13
>Bis: A Mailing list for WIEN2k users
>Betreff: [Wien] OMP_NUM_THREADS
>
>Dear Wien2k users,
>
>We were told in the WIEN workshop that for  mkl+multi-core cases, it might be better having a setting of $OMP_NUM_THREADS =2.
>
>I have two questions in my mind:
>
>Q1.  Does this apply to a 2 core system with 4GB RAM that is not running parallel calculation (not K-point parallel nor mpi-parallel )?
>
>
>Q2. Or this only apply to eg a quad core machine that runs on k-point parallel or mpi-parallel calculation?
>
>I have a 4-Core Dell T7500 PC with 12GB RAM, each core is of two threads, so in Susie/Linux or even in Windows, it all displays as a 8 CPU machine (so it is in actuality a four-core CPU but each core is with 2 threads, so all the OS sees it as a 8-core CPU). The actual info for this CPU is here if you like to see the details of it: http://ark.intel.com/products/37111
>
>I am setting up this machine running k-parallel calculation (not mpi-parallel as I have got only one of this machine for the moment), I am pondering:
>
>Which of the following 2 scenarios is a better choice for a 90 atom supercell calculation?
>
>Scenario  1.
>.machines files is this:
>-------
>granularity:1
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>extrafine:1
>----------
>and the OMP_NUM_THREADS=1 as default in my .bashrc file.
>so no multi-threading but all k-parallelism. (With this setting, I do notice after running the job for while - more than an hour say, the 8 CPUs shown in the System Monitor says only two CPUs were really utilized at a time (and it keep switching CPUs for the full-loading status, but mostly only two fully loaded at a time) and the rest of the 6 CPUs weren't really doing much - some of a few percentage of the load and others even on 0% - so I was wondering maybe this setting isn't optimized?
>
>Scenario  2.
>.machines files would be like this:
>-------
>granularity:1
>1:localhost
>1:localhost
>1:localhost
>1:localhost
>extrafine:1
>----------
>and set the OMP_NUM_THREADS=2 in my .bashrc file - I have not tried this setting as I am not sure if this would be a workable setting?
>
>Or, both settings would work and won't make much difference in calculation time length for a supercell calculation of 90 atoms? I am new to WIEN so I could not fully understand the THREAD'ings in WIEN's aspect.
>
>On addition, for the above two .machines file setting, would it make any difference if I put the real hostname in the place of "localhost"?
>
>Any comment would be greatly appreciated.
>
>Thank you!
>
>Kind regards,
>Qiwen
>
>**********************************************************
>
>Dr QiWen YAO
>
>JSPS Fellow
>Multifunctional Materials Group
>Optical and Electronic Materials Unit
>Environment and Energy Materials Research Division
>
>National Institute for Materials Science
>
>1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
>Phone: +81-29-851-3354, ext. no. 6482, Fax: +81-29-859-2501
>
>**********************************************************
>
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**********************************************************

Dr QiWen YAO

JSPS Fellow
Multifunctional Materials Group
Optical and Electronic Materials Unit
Environment and Energy Materials Research Division

National Institute for Materials Science

1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
Phone: +81-29-851-3354, ext. no. 6482, Fax: +81-29-859-2501

**********************************************************