On 2/10/07, Tang, Changqing <[EMAIL PROTECTED]> wrote: > > > > > >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 ? According to IBTA spec HCA will process WR entries in strict order in which they are posted so the send will block all WR posted after this send, Until-unless HCA has multiple processing elements, I think even then processing order will be maintained by HCA 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 > > > > > > > > _______________________________________________ > openib-general mailing list > [email protected] > http://openib.org/mailman/listinfo/openib-general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general > >
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