Usage of IbvMr.lKey vs. rKey on remote side when setting up WRITE/READ operation

[andymalakov]

Hi Patrick,

I noticed that samples send local memory region's LKey to remote side. That is on remote side we use local LKey in SVCPostSend.RdmaMod.setRkey(). This seems to go against Verbs API (which dictates use of RKey). But the strange fact is - examples work fine. Is there any explanation for this?

For example, JVerbsReadClient.java, line 80.

Thanks, Andy

[patrickstuedi]

Hi Andy,

In JVerbsReadServer line 70 (sendBuf.putInt(dataMr.getLkey()), the server passes the lkey of its buffer to the client. You're right, ideally the server should pass the rkey. In most cases the lkey and the rkey of a MR are equal so it wouldn't make a difference. Line 80 at the client (sendWR.getRdma().setRkey(lkey)) is simply using the key it received from the server and uses it to set the RDMA rkey which is correct. The fact that the local variable is called lkey is a bit unfortunate... otherwise the code is fine I think.

[andymalakov]

In most cases the lkey and the rkey of a MR are equal so it wouldn't make a difference

If that's the case let's close the issue. Thank you for clarification