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ProfileConan
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Message 65979 - Posted: 30 Nov 2016, 22:19:57 UTC

After a bit of an absence from the project I have come back to run some of the N-Body simulations after reading about it in an astronomy magazine.

I recently also started running an older 8 core/16 thread xeon server picked up cheaply.

I have been noticing a few things about these Multi-Threaded work units (mt).

The first thing you of course notice is the very low credit per work unit. Searching other results as well as mine I have seen as low as 1.48 credits for a WU and as high as 41 credits, with most around the 15 to 26 credit mark.

Second thing is this credit to some degree seems related to the benchmark figures.

Third thing is the more cores running the WU the less credit per hour you will get.
This is due to the extra CPU time run up by the extra cores.

A 4 core machine may take a RUN time of 800 seconds for a CPU time of 3,200 seconds (this is approximate).
My 16 core machine drops the RUN time to 500 seconds but the CPU time goes up to 8,000 seconds in doing so.

This then means that if 26 credits are awarded then the 4 core computer gets 29.25 cr/h and is doing OK, however my 16 core only gets 11.7 cr/h.

The WU's only run a short time, however a number get downloaded at once and take some time to work through, stopping my computer from running any other projects.

With credit per hour measured against CPU time not RUN time I don't get much reward for these work units.

Yes I could limit the number of cores being used but that is a lot of mucking around and will affect other projects that I run (which is over 2 dozen).

I was surprised that a Multi Threaded aplication is not awarding the effort of extra cores being used to solve the problem, less cores more reward.

So does this application become less efficient after a certain number of cores are reached? If so that should be stated to anyone wanting to run the application.

Thanks
Conan
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Message 65985 - Posted: 4 Dec 2016, 7:51:17 UTC


I was surprised that a Multi Threaded aplication is not awarding the effort of extra cores being used to solve the problem, less cores more reward.

So does this application become less efficient after a certain number of cores are reached? If so that should be stated to anyone wanting to run the application.


Yep same for me less credit and also when I run mt app 3/4 core my pc start laggy screen frozen and come back. So I stop crunching them.
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Message boards : Number crunching : Running N-Body work units

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