Artur Tyliszczak ha scritto:
> Hi Davide,
>
> Thanks a lot.
>
>>Hi Artur
>>
>>As it has already been pointed out in this list, if you have a plain SMP
>>system you should not worry much about on which socket/core your
>>parallel processes run within a single node, provided you have a recent
>>enough kernel (multicore/hyperthread aware) it will probably do a good
>>scheduling job.
>
> kernel 2.6.18.8-0.5 with suse 10.2 is it recent enough ?
Yes, I think so.
> I also did some tests and this is what I observed on 8 dual cores
> workstation (16 cores)
> When I run 2 jobs (mpirun -np 8 ./job_1 and mpirun -np 8 ./job_2)
> simultaneously then the execution time of each of them is about 20%
> longer than when I run these jobs consecutively, i.e. first mpirun -np 8
> ./job_1 and then when it finished mpirun -np 8 ./job_2. Is it common
> behavior?
I would say it is a good result! Dual core processors share part of the
surrounding hardware even more than dual processors do on PC boards
(other people on this list may explain better what is exactly shared by
cores, I mean cache, memory channels etc.) so I think it is really
unlikely to obtain 100% scaling with dual cores even on independent
applications, and losing 20% is really acceptable in my experience.
cheers, Davide
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