[Beowulf] Home beowulf - NIC latencies

Patrick Geoffray patrick at myri.com
Mon Feb 7 04:48:22 EST 2005


Hi Duncan,

duncan.roweth at quadrics.com wrote:
> This example reports the average time for 1000
> blocking get calls. Patrick's description of the
> mechanism is essentially correct, apart from the
> detail that we have a fast path for short operations
> that avoids the need to set up a DMA. 

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

The only way that I can think of is to map the host virtual memory into 
the NIC memory space and let all memory writes generates PIO writes to 
actually modify the NIC memory. Surely, you must be talking about 
another DMA.

Patrick
-- 

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