MPICH default buffer size

William Gropp gropp at
Mon Nov 18 10:56:23 PST 2002

At 09:25 AM 11/18/2002 -0800, khoa nguyen wrote:
>anyone knows what is the default buffer size of
>MPICH???  I knew LAM defaults to setting the OS socket
>buffering size of 64k, but I don't know what MPICH's
>Are there anyway I can check the buffer size available
>in my system?  I install MPICH tar bar, then ran
>configure with all default settings, so I don't know
>what is this buffer size currently set?  I search
>around MPICH header files but couldn't find it.
>Also, how can I change/reset this buffer size?

For the ch_p4 device, the default socket buffer size is 16k.  The reason 
for this choice is that some systems would fall back to truly pitiful sizes 
if the selected size exceeded some (also small) maximum.  The default sizes 
can be controlled by either changing the default set in 
mpich/mpid/ch_p4/p4/lib/p4_sock_util.h (SOCK_BUFF_SIZE), with the 
environment variable P4_SOCKBUFSIZE, or with the command-line argument 
-p4sctrl bufsize=64 (see the User's manual for other options and choices 
for controlling the socket read/write operations).


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