Global Shared Memory and SCI/Dolphin
kus at free.net
Mon Jul 23 12:44:16 EDT 2012
According to James Cownie
> > > Because MPI is what most people want to achieve code- and
> > > peformance-portability.
> > Partially I may agree, partially - not: MPI is not the best in the
> > sense of portability (for example, optimiziation requires knowledge
> > of interconnect topology, which may vary from cluster to cluster,
> > and of course from MPP to MPP computer).
> MPI has specific support for this in Rolf Hempel's topology code,
> which is intended to allow you to have the system help you to choose a
> good mapping of your processes onto the processors in the system.
Unfortunately I do not know about that codes :-( but for the best optimization I'll re-build the algorithm itself to "fit" for target topology.
> This seems to me to be _more_ than you have in a portable way on the
> ccNUMA machines, where you have to worry about
> 1) where every page of data lives, not just how close each process is
> to another one (and you have more pages than processes/threads to
> worry about !)
> 2) the scheduler choosing to move your processes/threads around the
Yes, but "by default" I beleive that they are the tasks of operating system,
or, as maximum, the information I'm supplying to OS, *after* translation
and linking of the program.
> > I think that if there is relative cheap and effective way to build
> > ccNUMA system from cluster - it may have success.
> Which is, of course, what SCI was _intended_ to be, and we saw how
> well that succeeded :-(
> -- Jim
> James Cownie <jcownie at etnus.com>
> Etnus, LLC. +44 117 9071438
Zelinsky Institute of Organic Chemsitry
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