[Beowulf] MPICH ch_p4 compile vs runtime options - bufsize, pkt_size, socksize

Bill Wichser bill at Princeton.EDU
Mon Aug 16 06:54:06 PDT 2004

Can anyone explain to me what the various options for MPICH compilation 
versus what the runtime options would provide?

For example, when compiling MPICH-1.2.6 I have the options:

which state "changes the size of the socket buffers used."

allows you to choose the message length at which the ADI switches from 
its short to long message format.

And for runtime I have:
a.out -p4sctrl bufsize=KBYTES
which controls the soket buffer size

The environment variables:
P4_SOCKBUFSIZE - defines the socket buffer size in bytes

Now in all cases I will also assume that the system-wide TCP settings 
have also been increased (net.core.[rw]mem_max, net.ipv4.tcp_[ rw]mem) 
in order to support sizes allowed in the above.

Except for optimizing -pkt_size I am under the belief that all the 
others are effectively one and the same.


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