Hi Charles,
Charles ROGE ha scritto:
> Hello,
>
> I tried the following to place LAM-MPI tasks on an SMP system.
>
> lamboot -v -ssi rpi usysv ./hostfile
>
> with cat ./hostfile
> toto cpu=16
>
> Then I tried to launch an application
> mpirun c8-15 ./a.out
>
> But it did not work, LAM-MPI tasks were not running on cpus 8-15.
What do you mean exactly by "tasks were not running on cpus 8-15":
nothing is running at all, or the task are not running on the requested
CPUs but on the others (0-7, I guess)?
If the first is true, then you probably have to check your LAM-MPI
installation or your application.
If the second holds, then your request is pointless, in my knowledge,
LAM does not make anything particular to attach processes to CPUs in a
SMP system, it just starts as many processes as requested, then it is up
to the operating system to balance them among the available processors,
this is the essence of Symmetric Multi Processing; AFAIK, there is no
such a concept (and no need too) of starting a process on a particular
CPU in a plain SMP system.
If you are using the Linux kernel, then recent versions should have a
tunable scheduler which tries to attach processes to CPUs as much as
possible (the so-called CPU affinity) to improve performance on SMP, but
it is not guaranteed either that a given process will always run on the
same CPU.
If you have a NUMA (Non Uniform Memory Access) system, then things are
more complex, but I have no direct experience of that.
Hope this helps, Davide
>
> Did I do something wrong?
> Does LMA-MPI placement work on SMP system?
>
> I am using lam-7.1.2
>
>
> Charles
>
>
> _______________________________________________
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>
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