[ofa-general] Question on IB RDMA read timing.

[Bharath Ramesh]

I wrote a simple test program to actual time it takes for RDMA read over
IB. I find a huge difference in the numbers returned by timing. I was
wondering if someone could help me in finding what I might be doing
wrong in the way I am measuring the time.

Steps I do for timing is as follows.

1) Create the send WR for RDMA Read.
2) call gettimeofday ()
3) ibv_post_send () the WR
4) Loop around ibv_poll_cq () till I get the completion event.
5) call gettimeofday ();

The difference in time would give me the time it takes to perform RDMA
read over IB. I constantly get around 35 microsecs as the timing which
seems to be really large considering the latency of IB. I am measuring
the time for transferring 4K bytes of data. If anyone wants I can send
the code that I have written. I am not subscribed to the list, if you
could please cc me in the reply.

Thanks,

Bharath

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Bharath Ramesh       <bramesh at vt.edu>       http://people.cs.vt.edu/~bramesh