High Performance TCP/IP communications with HPs and IBMs connected around an Ancor Fibre Channel Fabric

VI. Conclusion

Switching High Performance TCP/IP on workstations is really worthwhile, because it provides substantial improvements on the performance for TCP/IP communications.

Setting TCP_no_delay option or not during the tests has practically no influence on the bandwidth, which is generally measured for large packets. On the contrary, this option must be set to ensure a realistic overhead measurement. Unfortunately, it was seldom possible to run `Netperf' with TCP_no_delay option set for transmitting small messages (less than 1 Kbytes), because it was running out of memory (the maximum available memory space reserved for the network on a node was exceeded).

The following is a summary of the performances we measured, according to the hardware configuration used:

• - communications between IBM workstations: the overhead of the system is around 700 microseconds (measured with TCP_no_delay option set). When TCP_no_delay option was disabled, we measured an over optimistic value of 50 microseconds. The bandwidth can reach 11.25 Mbytes/s for transmitting 105 byte messages (for a 1 Mbyte socket buffer size).
  
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• - bi-directional communications between IBM workstations: a degradation of around 30% on average is reported, with regard to the expected performance.
  
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• - communications between HP workstations: the over optimistic overhead of the system is around 25 microseconds (measured without TCP_no_delay option set, because it ran out of memory), and the bandwidth can reach 10.5 Mbytes/s for transmitting 64 Kbyte messages (for a 349525 byte socket buffer size, which corresponds to the maximum size available with the current network configuration).
  
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• - communications between RS/6000 590 and HP/9000 700 workstations: the overhead of the system is around 25 microseconds (completely unrealistic because measured without TCP_no_delay option set), and the bandwidth can reach 10.3 Mbytes/s for transmitting 64 Kbyte messages (for a 349525 byte socket buffer size).
  

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