On 2/12/07, Devesh Sharma <[EMAIL PROTECTED]> wrote: > 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, post ordering accross QP is not guaranteed hence presence of same CQ or different CQ will not affect any thing. > > rather B and C are doing a long time RDMA_WRITE,or send/recv. But B If RDMA WRITE _on_ B, no effect on performance. If RDMA WRITE _on_ C, _may_ affect the performance, since load is on same HCA. In case of Send/Recv again _may_ affect the performance, with the same reason. > > must sends RNR periodically to A, right?. So does the pending message > > from A affects B's overall performance between B and C ? But RNR NAK is not for very long time.....possibly this performance hit you will not be able to observe even. The moment rnr_counter expires connection will be broken! > > > > 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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