Re: openMPI vs openMosix

absolutely. the issue of shm performance comes up every six months in
the openMosix mailing ilsts for these past six years, meanwhile the
underlying physics and simple queuing theory haven't changed much at
all.

Moshe



On 6/25/07, Wes Wagner <[email protected]> wrote:
> Is this not a classic, use the right tool for the right job issue? If you
> need massive scalable symmetric multi-processing, using a large SMP machine.
> If you can and need to do massive parallel multiple independent processes
> that share nothing, use a cluster or batch processing system.
>
> If you can't afford a massive SMP system, redefine the problem.. ?
>
> -Wes
>
>
> On 6/25/07, Moshe Bar < [email protected]> wrote:
> > 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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> Wes Wagner
>
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