[mcstas-users] MPI questions/bugs

[Jean-Francois.Moulin at hzg.de]

Hi dear McStas users/devel,

Here are some questions/bug reports which I put together as they might be related to each other

1) I am running into some trouble with longish (1e8 and above) simulations: the trace gives an ETA which is coherent (i.e it scales with the number of trajectories). I see that the progress bar follows the expected timing and then stays stuck forever at 90 % or so.
I am using MPI with 4 cores, and they are forever kept fully busy. 
This is a nasty problem it seems: does not always appear for the exact same setup.... 1.5e8 traj. seems to be a diffuse boundary for triggering the effect on my machine.

2) Moreover -small bug- it seems the progress bar has a conversion min <-> hours problem
(tested here with 1 core, but behaviour is similar with 4)
1e7   ETA 31 [s]
1e8   ETA 5.41667 [min] = ca 310 sec, OK
1e9   ETA 54.581 [min] OK
1e10 ETA 32457 [h] is exact if time would be in min... 
I am surely not the first one to notice though...

3) While trying to understand (1) I looked at the performance of the multiprocessor use: 
Using MPI I got the following timings for 1E8 trajectories

ncores  time (min)

1           5.333
2           2.95
3           2.9166
4           2.3333

a system monitor shows that the requested number of cores are running at 100% for the total time.
I do not have a large disk I/O activity.
From what I read in the manual I was expecting a very good scalability...

4) More a question then a bug: when using MPI  wavelength vs tof plots show a wrong pattern (when running single processor the pattern is ok). I noticed the warning concerning the use of the auto scale parameter together with MPI but I remember a discussion with Emmanuel Fahri where he mentioned that the errors in the outputs should be negligible... I put two images in attach to illustrate the difference I get. Both simulations are the same first with single machine, second on 4 procs.
Is this kind of behaviour really expected?  
I have not yet tried to use fixed parameters as this is rather un-practical...

5) last and least: minor but annoying for automatic analysis of the simulation files... 
mcstas.sim (sometimes) has a wrong date field based on EPOCH : 
Date:   Simulation started (0) Thu Jan  1 01:00:00 1970


I am running McStas 1.12c under Mint13 using opne MPI.


Thanks a lot for reading down to this point and possibly answering ;0)

Best 
Jean-Francois

-
Helmholtz Zentrum Geesthacht
Institut für Werkstoffforschung
Abteilung WPN, Instrument REFSANS
Lichtenbergstr. 1
85747 Garching FRM II
Tel.: +49 (0)89 289 10762
Internet: http://www.frm2.tum.deHelmholtz-Zentrum Geesthacht 
Zentrum für Material- und Küstenforschung GmbH 
Max-Planck-Straße 1 I 21502 Geesthacht I Deutschland/Germany 

Geschäftsführer/Board of Management: Prof. Dr. Wolfgang Kaysser, Dipl.-Ing. Michael Ganß 
Vorsitzender des Aufsichtsrates/Chairman of the Supervisory Board: MinDirig Wilfried Kraus 
Amtsgericht Lübeck HRB 285 GE (Register Court) 
Internet: http://www.hzg.de  
-------------- next part --------------
A non-text attachment was scrubbed...
Name: wl_tof_1core.png
Type: image/png
Size: 41513 bytes
Desc: not available
URL: <http://mailman2.mcstas.org/pipermail/mcstas-users/attachments/20121009/7ff46c3c/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: wl_tof_4cores.png
Type: image/png
Size: 45265 bytes
Desc: not available
URL: <http://mailman2.mcstas.org/pipermail/mcstas-users/attachments/20121009/7ff46c3c/attachment-0001.png>