A 3D example of KSPSolve?

[Shi Jin]

Here is the test on a linux cluster with gigabit
ethernet interconnect.
MPI2/output:Average time for MPI_Barrier():
6.00338e-05
MPI2/output:Average time for zero size MPI_Send():
5.40018e-05
MPI4/output:Average time for MPI_Barrier(): 0.00806541
MPI4/output:Average time for zero size MPI_Send():
6.07371e-05
MPI8/output:Average time for MPI_Barrier(): 0.00805483
MPI8/output:Average time for zero size MPI_Send():
6.97374e-05

Note MPI<N> indicates the run using N processes.
It seems that the MPI_Barrier takes a much longer time
do finish than one a SMP machine. Is this a load
balance issue or is it merely the show of slow
communication speed? 
Thanks.
Shi
--- Shi Jin <jinzishuai at yahoo.com> wrote:

> Yes. The results follow.
> --- Satish Balay <balay at mcs.anl.gov> wrote:
> 
> > Can you send the optupt from the following runs.
> You
> > can do this with
> > src/ksp/ksp/examples/tutorials/ex2.c - to keep
> > things simple.
> > 
> > petscmpirun -n 2 taskset -c 0,2 ./ex2 -log_summary
> |
> > egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 1.81198e-06
> Average time for zero size MPI_Send(): 5.00679e-06
> > petscmpirun -n 2 taskset -c 0,4 ./ex2 -log_summary
> |
> > egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 2.00272e-06
> Average time for zero size MPI_Send(): 4.05312e-06
> > petscmpirun -n 2 taskset -c 0,6 ./ex2 -log_summary
> |
> > egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 1.7643e-06
> Average time for zero size MPI_Send(): 4.05312e-06
> > petscmpirun -n 2 taskset -c 0,8 ./ex2 -log_summary
> |
> > egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 2.00272e-06
> Average time for zero size MPI_Send(): 4.05312e-06
> > petscmpirun -n 2 taskset -c 0,12 ./ex2
> -log_summary
> > | egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 1.57356e-06
> Average time for zero size MPI_Send(): 5.48363e-06
> > petscmpirun -n 2 taskset -c 0,14 ./ex2
> -log_summary
> > | egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 2.00272e-06
> Average time for zero size MPI_Send(): 4.52995e-06
> I also did 
>  petscmpirun -n 2 taskset -c 0,10 ./ex2 -log_summary
> |
> egrep \(MPI_Send\|MPI_Barrier\)
> Average time for MPI_Barrier(): 5.00679e-06
> Average time for zero size MPI_Send(): 3.93391e-06
> 
> 
> The results are not so different from each other.
> Also
> please note, the timing is not exact, some times I
> got
> O(1e-5) timings for all cases.
> I assume these numbers are pretty good, right? Does
> it
> indicate that the MPI communication on a SMP machine
> is very fast?
> I will do a similar test on a cluster and report it
> back to the list.
> 
> Shi
> 
> 
> 
> 
>  
>
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