Re: openMPI vs openMosix

not only is the normal RAM access a full 3 to 4 orders of magnitude
faster, but also there is simulatenous access to cache lines
resolution, whereas a shared mem implementation has to relay on the
MMU, which only does 4096 bytes as a minimum, which vastly increases
the true and false sharing conflicts.

To have a NIC help with that it would have to do something like RDMA,
with (at the least) MMU protection synced with the MMUs of all
connected nodes and remote interrupt capability. I doubt, however,
that such a dream NIC would help much in terms of performance. This
would be very close to the Altix solution, and witness their problems:
nodes have to be very close to each other (max 2 or 3 feet I think),
and

On 6/25/07, Christian Leber <[email protected]> wrote:
> On Mon, Jun 25, 2007 at 10:41:24AM -0500, Moshe Bar wrote:
> > we used to have it. Shared memory without hardware support very
> > severely limits the types of apps that will actually scale. Even sgi
> > in their altix machines (which are essentiallys shared memory
> > machines) have very limited scalability for a lot of apps, if not
> > most.
>
> What hardware features would be desireable to have in a NIC to be able
> to implement shared memory halfway fast for Mosix on page level?
>
> Regards
> Christian Leber
>
> --
> http://rettetdieti.vde-uni-mannheim.de/
>
>
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