Brian,
Thanks for replying... quick question. If I introduced
sleep() in profile function MPI_ISend() and have two
consecutive MPI_Isend(). Will the program thread
suspend itself in the first MPI_Isend()(due to
sleep()) before moving to the next MPI_Isend()? I
suppose it will. That kind of defeats the purpose as
far as my application is concerned..
Thanks
john
--- Brian Barrett <brbarret_at_[hidden]> wrote:
> On Mar 13, 2005, at 8:42 PM, John Korah wrote:
>
> > I am trying to simulate variable latency links on
> a
> > homogenous clusters. Meaning the latency of links
> > between certain pairs of computers are larger than
> > other links.
> >
> > Is there any way I can use MPI communication
> > primitives to do it? I am using sleep function to
> do
> > it now....
>
> Are you trying to simulate variable latency between
> MPI applications
> using only MPI primitives? LAM doesn't have a
> built-in feature for
> doing this (or doing bandwidth limiting or anything
> like that).
> However, you may be able to do what you want with
> the profiling layer
> and intercept MPI calls. For really simple
> simulations, sleeps in the
> profiling layer should fake latency differences.
> Since you know
> everything the MPI layer knows about the message
> being sent, you could
> do really complex things that I can't even imagine.
>
> For a detailed explanation of the MPI profiling
> layer, have a look at
> the MPI standard. But as a quick example, if you
> wanted to make
> MPI_Send take 1 second longer than usual, you could
> create an MPI
> profiling function like:
>
> int
> MPI_Send(void * buf, int count, MPI_Datatype dtd,
> int rank, int tag,
> MPI_Comm comm)
> {
> sleep(1);
> return PMPI_Send(buf, count, dtd, rank, tag,
> comm);
> }
>
> Then just compile like normal - your version of
> MPI_Send will be called
> then call PMPI_Send, which is another entry point
> into LAM/MPI.
>
> Hopefully, you can come up with something more
> creative than I can :).
>
> Brian
>
> --
> Brian Barrett
> LAM/MPI developer and all around nice guy
> Have an LAM/MPI day: http://www.lam-mpi.org/
>
> _______________________________________________
> This list is archived at
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>
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