Hello Scott,
thanks for your optimistic view :))
After this short discussion I think that the main problem
(considering just single GPU jobs) will be probably "just"
sufficient cooling ...
Best wishes,
Marek
Dne Tue, 13 Sep 2011 20:15:27 +0200 Scott Le Grand <varelse2005.gmail.com>
napsal/-a:
> AMBER is designed to run the entire simulation in GPU-space. The CPU
> acts
> as a glorified foreman shouting out directions to the GPU as to which
> tasks
> it should run. If AMBER were rewritten from the ground up, that role
> could
> be removed entirely. The upshot is that for single-GPU runs, you could
> probably stuff 8 GPUs into a single box and barely notice the difference.
> And you could also use a cheap consumer CPU as well since it's mostly
> sitting on its butt waiting on the GPU(s).
>
> The difference between using a 4 year-old $20 CPU and a current $1000+
> CPU
> in this situation is about 2-3%.
>
>
>
>
> 2011/9/13 Marek Maly <marek.maly.ujep.cz>
>
>> Hi Ross,
>>
>> first of all thanks a lot for your complex answer !
>> In fact I assume mainly independent single GPU jobs. So if I understood
>> well, in such case there should not be problem considering below
>> mentioned
>> motherboard/CPU/4xGPU. Am I right ?
>>
>> Best wishes,
>>
>> Marek
>>
>>
>>
>>
>> Dne Tue, 13 Sep 2011 18:53:34 +0200 Ross Walker <ross.rosswalker.co.uk>
>> napsal/-a:
>>
>> > Hi Marek,
>> >
>> > I would say that the answer is, with caveats, not really. The reason
>> for
>> > this is not a core to GPU ratio argument per se but actually one of
>> > memory
>> > bandwidth. For a single socket motherboard there is no way that it can
>> > drive
>> > 4 PCI-E sockets flat out at x16 speed. Hence you are always going to
>> get
>> > contention. Typically I would say never go beyond 2 GPUs per node for
>> a
>> > single socket system. 4 GPUs per node is pushing it for a dual socket
>> > system
>> > even with the highest CPU FSB speed you can get so on a single socket
>> > system
>> > with a low end CPU it is definitely not going to cut it.
>> >
>> > Now if you only plan to run single GPU jobs. I.e. 4 independent jobs
>> at
>> > once
>> > with reasonably large values for ntpr, ntwx etc then it is probably
>> not
>> > an
>> > issue since the memory bandwidth only really comes into play at each
>> > output
>> > file or trajectory write for most types of calculations. However,
>> trying
>> > to
>> > run in parallel where a single job spans GPUs it really all comes down
>> > to a
>> > combination of the aggregate memory bandwidth of the main CPU memory
>> per
>> > GPU
>> > and the PCI-E bandwidth to each GPU when all are communicating flat
>> out
>> > at
>> > the same time. You might be able to get speedup across 2 of the GPUs
>> if
>> > you
>> > leave the other two idle. However, running two sets of dual GPU runs
>> or
>> > running a single 4 GPU run is likely to cause so much contention that
>> see
>> > little or no speedup.
>> >
>> > So it really comes down to a case of the type of jobs you want to run.
>> >
>> > I hope that helps.
>> >
>> > All the best
>> > Ross
>> >
>> >> -----Original Message-----
>> >> From: Marek Maly [mailto:marek.maly.ujep.cz]
>> >> Sent: Tuesday, September 13, 2011 7:19 AM
>> >> To: amber.ambermd.org
>> >> Subject: [AMBER] Sufficient CPU cores/GPU ratio ?
>> >>
>> >> Hi all,
>> >>
>> >> just a very quick technical question. I would like to know if 4 core
>> >> CPU
>> >> "Intel Core i7-960" might be sufficient for
>> >> 4 GPU machine (motherboard: Asus P6T7 WS SuperComputer - Intel X58
>> ).
>> >> I
>> >> mean if ratio 1 CPU core/ 1 GPU might
>> >> be here sufficient also considering some requirements (on CPU) for
>> >> managing operating system etc.
>> >>
>> >> Thanks in advance for any relevant comment !
>> >>
>> >> Best wishes,
>> >>
>> >> Marek
>> >>
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>> > http://www.eset.cz
>> >
>> >
>> >
>>
>>
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>
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>
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>
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Received on Tue Sep 13 2011 - 11:30:08 PDT
