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Subject: Re: [OMPI devel] Affect of compression on modex and launch messages
From: Gleb Natapov (glebn_at_[hidden])
Date: 2008-04-07 10:13:49

On Mon, Apr 07, 2008 at 07:54:38AM -0600, Ralph H Castain wrote:
> On 4/7/08 7:45 AM, "Gleb Natapov" <glebn_at_[hidden]> wrote:
> > On Mon, Apr 07, 2008 at 07:28:07AM -0600, Ralph H Castain wrote:
> >>> Also can you explain how
> >>> allgather is implemented in orte (sorry if you already explained this once
> >>> and I missed it).
> >>
> >> The default method is for each proc to send its modex data to its local
> >> daemon. The local daemon collects the messages until all of its local procs
> >> have contributed, then sends the collected data to the rank=0 application
> >> proc. One rank=0 has received a message from every daemon, it xcasts the
> >> collected result to all procs in its job.
> >>
> > Only collected result is compressed or messages from each proc to local
> > daemon and messages from local daemon to rank=0 are compressed too?
> The individual inbound messages are not currently compressed prior to
> sending - too small to bother
Make sense.

> > Also I think if rank=0 will compress each modex message during
> > receive it can save some work during xcast.
> Seems to me like one compress of the entire message has to be a great deal
> faster than N compressions of N small messages...
The idea is that modex receive and compress will overlap.