On Mon, 2018-12-31 at 13:44 -0500, Chuck Lever wrote: > > On Dec 31, 2018, at 1:09 PM, Trond Myklebust < > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > > On Thu, 2018-12-27 at 17:34 -0500, Chuck Lever wrote: > > > > On Dec 27, 2018, at 5:14 PM, Trond Myklebust < > > > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > On Dec 27, 2018, at 20:21, Chuck Lever < > > > > > chuck.lever@xxxxxxxxxx> > > > > > wrote: > > > > > > > > > > Hi Trond- > > > > > > > > > > I've chased down a couple of remaining regressions with the > > > > > v4.20 > > > > > NFS client, > > > > > and they seem to be rooted in this commit. > > > > > > > > > > When using sec=krb5, krb5i, or krb5p I found that multi- > > > > > threaded > > > > > workloads > > > > > trigger a lot of server-side disconnects. This is with TCP > > > > > and > > > > > RDMA transports. > > > > > An instrumented server shows that the client is under-running > > > > > the > > > > > GSS sequence > > > > > number window. I monitored the order in which GSS sequence > > > > > numbers appear on > > > > > the wire, and after this commit, the sequence numbers are > > > > > wildly > > > > > misordered. > > > > > If I revert the hunk in xprt_request_enqueue_transmit, the > > > > > problem goes away. > > > > > > > > > > I also found that reverting that hunk results in a 3-4% > > > > > improvement in fio > > > > > IOPS rates, as well as improvement in average and maximum > > > > > latency > > > > > as reported > > > > > by fio. > > > > > > > > > > > > > Hmm… Provided the sequence numbers still lie within the window, > > > > then why would the order matter? > > > > > > The misordering is so bad that one request is delayed long enough > > > to > > > fall outside the window. The new “need re-encode” logic does not > > > trigger. > > > > > > > That's weird. I can't see anything wrong with need re-encode at > > this > > point. > > I don't think there is anything wrong with it, it looks like it's > not called in this case. So you are saying that the call to rpcauth_xmit_need_reencode() is triggering the EBADMSG, but that this fails to cause a re-encode of the message? > > > Do the window sizes agree on the client and the server? > > Yes, both are 128. I also tried with 64 on the client side and 128 > on the server side. That reduces the frequency of disconnects, but > does not eliminate them. > > I'm not clear what problem the logic in xprt_request_enqueue_transmit > is trying to address. It seems to me that the initial, simple > implementation of this function is entirely adequate..? I agree that the fair queueing code could result in a reordering that could screw up the RPCSEC_GSS sequencing. However, we do expect the need reencode stuff to catch that. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
