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IV. Communication Benchmarks

All measurements, whose aim is to determine overheads, communication latencies and throughputs at the user level, have been achieved on the sender side. We defined overheads, communication latencies and throughputs as follows:

The program used to test out communication performances, when using TCP/IP protocols, was Netperf. On all machines, we configured the High-Speed TCP/IP Extension (rfc 1323) to increase the performance of TCP/IP over Fibre Channel. Other appropriate network options were modified to fully utilize the advantages of rfc 1323, like for instance the maximum socket buffer size (sb_max), the window size on both receiver and sender sides (tcp_sendspace, tcp_revcspace), ... [see appendix on how to configure network options].

The TCP_no_delay option (-D) was set on the sender side: it is necessary for relevant measurements because it disables the so-called Nagle mechanism for the buffering (it avoids buffering and grouping messages before sending). Sometimes, we got some troubles when using this option turned on and we were obliged to turn it off (only in case of sending large messages with large socket buffers).

For the light-weight protocol (Raw Socket), no program was available from the public domain; therefore we used and ran an IBM hand-made application, which was evolved jointly by Carlo Miron and Massimo Bernaschi.

RD11 - 22 JUN 95
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