Artur Tyliszczak wrote:
> 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 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?
Yes, as Artur pointed out, the jobs will compete with each other for use
of the memory buss. This is probably done more efficiently if you
assign the 2 jobs to separate groups of nodes. All job schedulers used
with MPI have such options. Even then, they are likely to compete for
access to shared file systems.
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