[openib-general] IBV_WC_LOC_LEN_ERR in ibv_pingpong for message < 4KB

[Roland Dreier]

    Sayantan> Hi, If I run `ibv_pingpong' with msg size argument <
    Sayantan> 4096, I am encountering a IBV_WC_LOC_LEN_ERR. I have
    Sayantan> pasted the output from my run. Is this usage correct? Is
    Sayantan> anybody else getting the same error too?

Are you passing the --size argument to both the client and server
ibv_pingpong programs?  If not, then one side will post a receive
buffer too small to receive the message that the other side sends, and
you will get a local length error.

    Sayantan> If I may ask, what do the messages like:

    Sayantan>   [ 0] 00860404

    Sayantan> mean? They are not coming from `ibv_pingpong' but from
    Sayantan> somewhere else.  Are they supposed to be debug messages? 
    Sayantan> If yes, how can I interpret them?

That's temporary debugging code from libmthca, specifically the CQ
polling code.  It's dumping out the 32 byte CQ entry written by the
HCA hardware.  You will need Mellanox documentation to interpret it
(or you can just read the code in libmthca/src/cq.c).

 - R.