Thanks for the response. May be I am wrong. However my argument is as
follows: our test shows that a 100^3 grid per core performs 10 times
faster (normalised in proper unit) than 200^3. Both of these sizes
are not fitting in cache. 100^3 run is benefiting due to smaller size
where compiler is guessing access pattern in slightly better way.
So, in case of running one large job of 200^3 per core if I
oversubscribe the core with smaller jobs of size comparable to 100^3,
high saving due to better memory access should compensate for thread
On Mon, Dec 26, 2011 at 10:31 PM, Matthieu Brucher
> If your problem is memory bound and if you don't use the whole memory
> capacity of one node, it means that you are limited by your memory
> bandwidth. In this case oversubscribing the number of processes will lead to
> worse behavior, as all processes will fight for the same memory bandwidth.
> Just my opinion.
> Matthieu Brucher
> 2011/12/23 Santosh Ansumali <ansumali_at_[hidden]>
>> Dear All,
>> We are running a PDE solver which is memory bound. Due to
>> cache related issue, smaller number of grid point per core leads to
>> better performance for this code. Thus, though available memory per
>> core is more than 2 GB, we are able to good performance by using
>> less than 1 GB per core.
>> I want to know whether oversubscribing the cores can potentially
>> improve performance of such a code. My thinking is that if I
>> oversubscribe the cores, each thread will be using less than 1 GB so
>> cache related problems will be less severe. Is this logic correct or
>> due to cache conflict performance will deteriorate further?
>> In case, over-subscription can help, how shall I modify
>> submission file (using sun grid engine) to enable over-subscription of
>> my current submission file is written as follows
>> #$ -N first
>> #$ -S /bin/bash
>> #$ -cwd
>> #$ -e $JOB_ID.$JOB_NAME.ERROR
>> #$ -o $JOB_ID.$JOB_NAME.OUTPUT
>> #$ -P faculty_prj
>> #$ -p 0
>> #$ -pe orte 8
>> /opt/mpi/openmpi/1.3.3/gnu/bin/mpirun -np $NSLOTS ./test_vel.out
>> Is it possible to allow over-subscription by modifying submission file
>> itself? Or do I need to change hostfiles somehow?
>> Thanks for your help!
>> Best Regards
>> Santosh Ansumali,
>> Faculty Fellow,
>> Engineering Mechanics Unit
>> Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR)
>> Jakkur, Bangalore-560 064, India
>> Tel: + 91 80 22082938
>> users mailing list
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