Any news on Infiniband ?

Patrick Geoffray patrick at myri.com
Wed Feb 26 17:52:37 EST 2003


Hi Tony,

On Wed, 2003-02-26 at 16:46, Anthony Skjellum wrote:
> Because people ask for polling latency (it is not the right model for most
> real applications), we did provide this number.  We have found almost universal
> advantage to avoid polling MPI in almost all networks, including Ethernet+TCP
> Giganet, and Myrinet. 

Can you detail ? Unless you oversubscribed you processors, I don't see
the point. 
It may just be a side effect of your implementation: if you implement
the progression with some threads, sure you want to block to not waste
cycle in this progression threads. If you progress in the hardware,
blocking on interrupt is useless unless you oversubscribe your
processors and so you want to force the context switches.
Does IB offers hooks to progress the MPI protocol in hardware ?

> Our white paper shows the polling and non-polling implementation curves for
> bandwidth.  We normally encourage people not to use polling mode, where
> overhead is low. 

If your metric is bandwidth, you don't care about the interrupt
overhead: it's completely hidden by the communication cost because
bandwidth usually means large messages.

One of the flaws of IB is to use a paradigm built on VI. MPI did not map
well on VI, and I expect the same thing for IB.

Patrick
-- 

Patrick Geoffray, Phd
Myricom, Inc.
http://www.myri.com

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