Sorry I misread your original post. You are correct. The wqe->iova is
only used to fill in the RETH header so it is not needed after
the first packet.
This commit looks OK.
On Tue, May 3, 2022 at 2:59 PM Chengguang Xu <cgxu519@xxxxxxxxxxxx> wrote:
>
> 在 2022/5/3 1:15, Pearson, Robert B 写道:
> >> -----Original Message-----
> >> From: Chengguang Xu <cgxu519@xxxxxxxxxxxx>
> >> Sent: Monday, May 2, 2022 12:39 AM
> >> To: zyjzyj2000@xxxxxxxxx; jgg@xxxxxxxx; leon@xxxxxxxxxx
> >> Cc: linux-rdma@xxxxxxxxxxxxxxx; Chengguang Xu <cgxu519@xxxxxxxxxxxx>
> >> Subject: [RFC PATCH] RDMA/rxe: skip adjusting remote addr for write in retry operation
> >>
> >> For write request the remote addr will be sent only with first packet so we don't have to adjust wqe->iova in retry operation.
> > This is problematic for lossy networks. A very large read request, say 8MiB, sends 2048 packets in response without any acknowledgement
> > from the requester. If the packet loss rate was 1% the read request would never finish as the probability of sending 2048 packets without
> > loss is very small. The way the code works today is that the iova is adjusted, and if you are lucky the responder has already finished the
> > previous read operation and starts over with a new read reply starting with a first packet at iova. If you are less fortunate the previous
> > read reply has not finished and the responder will continue to work on it until it is finished before looking at the new read request wqe.
> > the completer will respond to each out of order packet by checking to see if it should start a retry but since it has already done so
> > it drops the packet. It's messy but one can make forward progress ~100 packets at a time. It would be faster if the responder saw that
> > the new request replaced the old one and stopped sending packets on the old read. I have no idea how CX NICs do this but just restarting
> > from scratch seems bad.
>
> I agree that read request indeed needs to adjust iova during retry and
> the adjustment(for read) has already done in below logic in req_retry().
>
>
> if (mask & WR_READ_MASK) {
> npsn = (wqe->dma.length - wqe->dma.resid) /
> qp->mtu;
> wqe->iova += npsn * qp->mtu;
> }
>
> For write request, retry will not send new iova because only first write
> packet has RXE_RETH_MASK regardless iova adjustment.
> Am I missing something?
>
>
> Thanks,
> Chengguang
>
>
>
>
>
