On Apr 27, 2009, at 9:14 AM, Underwood, Keith D wrote:

For many (most?) science and engineering codes, the trade-off between matching for two sided and synchronization for one sided is at best a wash, and often would fall in favor of two sided. There is, of course, an exception....

If one sided delivered truly stellar performance in terms of message rate and latency, you could (in some cases) eliminate the cost of the copy at the sender that is tyically done to send long messages to cover the overhead. The hardware to deliver that level of performance is truly rare...

Keith

"cost of the copy at the sender that is tyically done to send long messages to cover the overhead" ? Typically, any HPC NIC uses zero-copy for large messages. Copy is only used for small messages (where small depends on the fabric/NIC/ software stack). It is even possible to avoid copy on send for large messages over standard Ethernet using sendfile() and other options. Scott