NFS issues since upgrading to 13-RELEASE

Rick Macklem rmacklem at
Sun Apr 25 13:06:20 UTC 2021

Chris Roose wrote:
> Jason Unovitch wrote:
> > Does anything change if you set -tso -lro on the serving NIC on your
> > FreeBSD server side?  Do the Linux clients remain responsive then?
> Thank you, Jason. This seems to have cleared the problem up for me.
> Since disabling TSO and LRO on the server NIC last night, I haven't seen
>  any timeouts.
I think there might be a couple of reasons that disabling TSO resolves this:
1 - The obvious one is that the net chip/driver is broken for certain TSO
      segments. Often the culprit is a NFS read reply of just less than 64K,
      that is made up of a chain of 33mbufs with a total length just under
      64K. Then the driver adds a MAC layer header that bumps the size up
      to greater than 64K.
      --> This can happen if the driver does not set the TSO sizing parameters
            quite correctly, among other things.

2 - TSO does work correctly, but results in different timing of the TCP
      segments transmitted for the segment compared with non-TSO.

I believe that, for otis@, disabling TSO reduced the frequency of Linux
client hangs, but did not stop them.
--> reverting the patch in r367492 (this patch is not in FreeBSD12) has
       fixed the problem for him.


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