Re: [myrinet] What's the Fastest roundtrip communication using GM ?

Hello, Geoge -

Please refer to the description of GM_FAST_xxx events in
the section "Receiving Messages" in the GM API document,
http://www.myri.com/scs/GM/doc/gm_toc.html .  The basic idea
is that GM will automatically deliver "small messages" in the
form of FAST messages, which are not delivered to user space
(unless the user program specifically acts to cause this by
calling gm_unknown() or gm_memorize_message()).  By default,
a FAST message remains encapsulated in the receive event
struct, in LANai SRAM.

The definition of "small message" is not specified in the
document; it's left as an internal detail that may change.
As of the last time I checked, a "small message" was any
message of 120 bytes or less.

It would be relatively simple to write a little test program
to probe for the cut-off size.


Hope this helps.

- Max Stern
  Myricom