BIP performance curves

The BIP implementation make the reasonable assumption that the Myrinet hardware is reliable, and do provide to the application reliable in-order delivery of messages . Nevertheless BIP implementation do check that no error occur and will detect such errors, should they happen. In this very unlikely case it will not be able to for instance do automatic retransmission and so will abort the application.(note that since we started our platform we have never seen any error on our Myrinet network).

BIP latency

On the figure above, the first curve named "raw latency" represent the raw latency measured as explained on the previous page.

The second curve named "real usage" represent the time as measured by taking into account the filling of the buffer passed to bip_send wih some pseudo-random value, and the time to read after the bip_recv each value of the buffer (and checking it is the expected value).

Note also that the precise timings may depend on the position on the stations on the Myrinet switch, and wether you are using SAN Myrinet links, or LAN links. Depending on what pair of stations we are using, we can have transmission time about half a microsecond longer that those on the figures.

BIP bandwidth

This figure show the surprising bandwidth sustained by BIP even for medium message size. The same measurement method is again used.

BIP adaptive strategy

The BIP implementation cut a message into packet starting from a certain size, the size of the packets use depends heavily on the message length. The graph below represent the bandwidth obtained with our implementation with a fixed 256 bytes packet size, a fixed 4096 packet size, or our normal default adaptive strategy.

Clearly there no fixed packet size compromise possible that allow a close to the optimal transmission time, only an adaptive strategy maximize both asymptotic bandwidth and medium message transmission time.

Results table

Here are some numerical results corresponding to the above curves.

Message size (bytes)	Elapse Time (one-way)	Bandwidth (Mbytes/s)
0	4.30979	0
4	4.70473	0.85021
8	4.75908	1.68100
16	5.00942	3.19398
32	5.66980	5.64394
64	6.43804	9.94091
128	8.37586	15.2820
256	22.7809	11.2375
512	26.3253	19.4490
1024	33.9122	30.1957
2048	45.7438	44.7711
4096	68.9930	59.3684
8192	115.993	70.6248
16384	185.614	88.2692
32768	325.458	100.683
65536	603.300	108.629
131072	1131.45	115.844
262144	2189.34	119.736
524288	4297.29	122.004
1048576	8499.36	123.371
2097152	16830.30	124.605
4194304	33404.30	125.562
8388608	66507.70	126.130

Last modified: Thu Aug 21 13:44:26 CEST 1997   © BIP team