IP Multicast over Myrinet

Hello,

I am trying to do IP Multicasting over Myrinet  between 3 Linux machines
in a multi-pc renderer in the quest for higher b/w.

The three machines are connected to 2 networks each. 

* a Gigabit ethernet interface ( which goes to the outside world )
* a Myrinet switch ( local - connection between the 3 machines   ) 

We want the application to use the Gigabit interface for incoming traffic 
and the myrinet interface solely for IP Multicasting from Host A to B & C.


We had to put a static route in the routing table of Host A to do this
asking all Multicast traffic from Host A to go out on the myrinet
interface.

HOWEVER we still have a PROBLEM,

IP Multicasting over Myrinet is much slower compared to IP
Multicast over the Gigabit Ethernet.

Here are some nos. : 

Multicast Sender ( Host A ): 

UDP Packet size is 1425 bytes ( assuming MTU of 1500 bytes )
MYRINET : Sender sends 3.5 Mbytes in 0.02 seconds ( 1400 Mbits/sec )
GIGABIT : Sender sends 3.5 Mbytes in 0.04 seconds ( 700 Mbits/sec  )

These numbers roughly match the netperf tests below.


Multicast Receiver ( Host B ): 

MYRINET : Receiver reads 5 packets in 0.0018 seconds.
GIGABIT : Receiver reads 5 packets in 0.00011 seconds.

As a result while using myrinet, data is lost ( UDP packets are dropped or
overwritten in the sender buffer since the receiver is much slower
compared to the sender.


So I think if the problem of the slow read on the receiver is fixed, the
problem of packet loss will automatically be fixed.


I will be really glad if someone can tell me how to fix this problem,
Thanks in advance,
Sudipta


------------------------------------------------------------------------
NETPERF TESTS 
------------------------------------------------------------------------


TEST THE GIGABIT ETHERNET.

-m packet size,
-W buffer size,

netperf -H <dest> -tUDP_STREAM -- -m 1400 -W 262142

UDP UNIDIRECTIONAL SEND TEST to hires42-tn
Socket  Message  Elapsed      Messages                
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

262142    1400   10.00      851570      0     953.98
262142           10.00      840423            941.49

-----------------------------------------------------------------------

TEST THE MYRINET INTERFACE

netperf -H <test> -tUDP_STREAM -- -m 1400 -W 262142
UDP UNIDIRECTIONAL SEND TEST to hires42-m
Socket  Message  Elapsed      Messages                
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

262142    1400   10.00     1464232      0    1640.50
262142           10.00      383488            429.65

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