> >
> >Not for the receiver, but the sender will be severely slowed down by
> >having to wait for the RNR timeouts.
>
> RNR = Receiver Not Ready so by definition, the data flow
> isn't going to
> progress until the receiver is ready to receive data. If a
> receive QP
> enters RNR for a RC, then it is likely not progressing as
> desired. RNR
> was initially put in place to enable a receiver to create
> back pressure to the sender without causing a fatal error
> condition. It should rarely be entered and therefore should
> have negligible impact on overall performance however when a
> RNR occurs, no forward progress will occur so performance is
> essentially zero.
Mike:
I still do not quite understand this issue. I have two
situations that have RNR triggered.
1. process A and process B is connected with QP. A first post a send to
B, B does not post receive. Then A and B are doing a long time
RDMA_WRITE each other, A and B just check memory for the RDMA_WRITE
message. Finally B will post a receive. Does the first pending send in A
block all the later RDMA_WRITE ? If not, since RNR is triggered
periodically till B post receive, does it affect the RDMA_WRITE
performance between A and B ?
2. extend above to three processes, A connect to B, B connect to C, so B
has two QPs, but one CQ. A posts a send to B, B does not post receive,
rather B and C are doing a long time RDMA_WRITE, or send/recv. But B
must sends RNR periodically to A, right?. So does the pending message
from A affects B's overall performance between B and C ?
Thank you.
--CQ
>
> Mike
>
>
>
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