[mpich-discuss] Program uses 100% with MPICH2 (<10% with MPICH1)

Pavan Balaji balaji at mcs.anl.gov
Wed Jul 25 19:41:15 CDT 2012

Hi João,

On 07/25/2012 12:43 PM, asco developer wrote:
> Thanks for answering. I have tried both of your suggestions, 1) using
> one slave process per core and also 2) recompiling with configure
> option '--with-device=ch3:sock'. On both of them the MPI program still
> uses 100% CPU.

If you are seeing 100% CPU usage with ch3:sock, then the problem is 
something different.  Can you answer the following questions --

1. What is the mpiexec command-line you are using?

2. How many cores/nodes does your system have?

3. Does your program use threads (pthreads or OpenMP)?

> Based on the above, I have a set of questions, which I would
> appreciate if you could answer. Is this the expected behavior from any
> MPICH2 program? Do all MPICH2 work this way? Is there anything that I
> should change from the programing point of view in the? Currently, I
> use MPI_Scatterv as away of distributing the array among the
> processes. Do you need any information to better anser my questions?
> If yes, let me know.

MPICH2 should always be faster and more stable than MPICH1, unless you 
have more processes/threads than number of cores.

> I tempted to think that If there is nothing to do about it and at
> least for the application I'm using, MPICH1 seems to be a better fit
> than MPICH2. Do you agree is this last sentence?

I don't think that's true.  There's something silly going on over here, 
and we should try to figure it out.

  -- Pavan

Pavan Balaji

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