I think the main savings is that mellanox hardware works better when
fewer qp's are open. I.e., it's a resource issue on the HCA, not
necessarily a savings in posting buffers to the qp.
But it's quite a complicated issue. :-)
Gleb has some reservations about XRC; I'll let him expound on them...
On Jan 18, 2008, at 1:06 AM, Don Kerr wrote:
Those pointers were perfect thanks.
It easy to see the benefit of fewer qps (per node instead of per peer)
and less consumption of resources the better but I am curious about
the
actual percentage of memory footprint decrease. I am thinking that the
largest portion of the footprint comes from the fragments. Do you have
any numbers showing the actual memory footprint savings when using
xrc?
Just to be clear, I am not asking for you or anyone else to generate
these numbers, but if you had them already I would be curious to know
the over all savings.
-DON
Pavel Shamis (Pasha) wrote:
Here is paper from openib http://www.openib.org/archives/nov2007sc/XRC.pdf
and here is mvapich presentation
http://mvapich.cse.ohio-state.edu/publications/ofa_nov07-mvapich-xrc.pdf
Button line: XRC decrease number of QPs that ompi opens and as result
decrease ompi's memory footprint.
In the openib paper you may see more details about XRC. If you need
more
details about XRC implemention
in openib blt , please let me know.
Instead
Don Kerr wrote:
Hi,
After searching, about the only thing I can find on xrc is what it
stands for, can someone explain the benefits of open mpi's use of
xrc,
maybe point me to a paper, or both?
TIA
-DON
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Cisco Systems
