Good day to all,

I had run point to point osu_latency test in two nodes for 200 times.  Followings are the average time in microsecond for various size of the messages -

1KB    84.8514 us
2KB    73.52535 us
4KB    272.55275 us
8KB    234.86385 us
16KB    288.88 us
32KB    523.3725 us
64KB    910.4025 us

From the above looks like, 2KB message has less latency than 1 KB and 8KB has less latency than 4KB.

I was looking for explanation of this behavior  but did not get any.

1. MPIR_CVAR_CH3_EAGER_MAX_MSG_SIZE is set to 128KB. So none of the above message size is using Rendezvous protocol. Is there any partition inside eager protocol (e.g. 0 - 512 bytes, 1KB - 8KB, 16KB - 64KB)? If yes then what are the boundaries for them? Can I log them with debug-event-logging?
   

Setup I am using:

- two nodes has intel core i7, one with 16gb memory another one 8gb

- mpich 3.2.1, configured and build to use nemesis tcp

- 1gb Ethernet connection

- NFS is using for sharing

- osu_latency : uses MPI_Send and MPI_Recv

- MPIR_CVAR_CH3_EAGER_MAX_MSG_SIZE= 131072 (128KB)

Can anyone help me on that? Thanks in advance.

Best Regards,

Abu Naser

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