[Beowulf] Home beowulf - NIC latencies

[duncan.roweth at quadrics.com]

Patrick

Thanks for your mail. 

> How can you do one-sided operations without a DMA on the 
> target side ?!?

Gets are done by telling the remote adapter to perform 
a put back to the source. This can be a request to start
a DMA (for large transfers) or it can be a request to the 
the Short Transaction ENgine (STEN).

The STEN is a fast path for short puts that can be used 
from either the main CPU or from the adapter. It can 
generate network packets from a stream of commands and
data written either by the main CPU (as PIO writes) or
directly by the adapter. 

There are more details are in the "Hot Chips" paper that 
we wrote with Fabrizio Petrini of Los Alamos. 

http://www.c3.lanl.gov/~fabrizio/papers/hot03.pdf


Best Wishes
Duncan Roweth
Quadrics Limited