[MPICH] An idle communication process use the same CPU as computation process on multi-core chips

[Reuti]

Hi,

Am 14.09.2007 um 00:41 schrieb Yusong Wang:

> I have a program which is implemented with a master/slave model and  
> the
> master just do very little computation. In my test, the master spent
> most of its time to wait other process to finish MPI_Gather
> communication (confirmed with jumpshot/MPE). In several tests on
> different multi-core chips (dual-core, quad-core, 8-core), I found the
> master use the same amount of CPU as the slaves, which should do  
> all the
> computation.

what do you mean in detail - you have let's say the master process  
running and 4 slaves and see a CPU usage of 500% on a machine with 8  
cores?

Having his programming style, you need a special configured  
machinefile if you use a queuing system, as otherwise one idling slot  
will be wasted for the master process.

-- Reuti


> . There are only two exceptions that the master use near 0%
> CPU (one on Window, one on Linux), which is what I expect. The tests
> were did on both Fedora Linux and Widows with MPICH2 (shm/nemesis
> mpd/smpd). I don't know if it is a software/system issue or caused by
> different hardware. I would think this is  (at least )related with
> hardware. As with the same operating system, I got different CPU usage
> (near 0% or near 100%) for the master on different multi-core nodes of
> our clusters.
>
> Is there any documents I can check out for this issue?
>
> Thanks,
>
> Yusong