[libfabric-users] ibv_post_send() execution time

Cheng Wang wangchenghku at gmail.com
Fri Sep 2 11:00:52 PDT 2016


I measured the execution time of ibv_post_send() in both rping program
and ib_write_lat program. Below is my pseudo code:

clock_gettime(); // start
clock_gettime(); // end

Specifically, I measured IBV_WR_RDMA_WRITE operation using the same data
size in Reliable Connection (RC) mode.

And the result shows each ibv_post_send() in rping takes around 170~180
nanoseconds to return, but in ib_write_lat program it only takes around 60
nanoseconds to return in average.
I suspected that this is caused by memalign of the sent buffer in
ib_write_lat. But after I changed the rdma sent buffer in rping to be also
memory aligned, it still takes around 170 nanoseconds.

May I know what caused this difference?

Many thank in advance.
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