Date: Sun, 25 Apr 2021 13:06:11 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Chris Roose <chrisroose@fastmail.com>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org> Cc: Juraj Lutter <otis@freebsd.org> Subject: Re: NFS issues since upgrading to 13-RELEASE Message-ID: <YQXPR0101MB09685508380CC691A95898BDDD439@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <089ce08a-1c77-b7a5-4e20-b1c22df23176@fastmail.com> References: <CABW2x9ooC0w4_50Rd3XfLQdKXrUtJEty6mbYmyMSAk7%2BWyyDpA@mail.gmail.com>, <089ce08a-1c77-b7a5-4e20-b1c22df23176@fastmail.com>
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Chris Roose wrote:=0A=
> Jason Unovitch wrote:=0A=
> > Does anything change if you set -tso -lro on the serving NIC on your=0A=
> > FreeBSD server side? Do the Linux clients remain responsive then?=0A=
>=0A=
> Thank you, Jason. This seems to have cleared the problem up for me.=0A=
> Since disabling TSO and LRO on the server NIC last night, I haven't seen=
=0A=
> any timeouts.=0A=
I think there might be a couple of reasons that disabling TSO resolves this=
:=0A=
1 - The obvious one is that the net chip/driver is broken for certain TSO=
=0A=
segments. Often the culprit is a NFS read reply of just less than 64K=
,=0A=
that is made up of a chain of 33mbufs with a total length just under=
=0A=
64K. Then the driver adds a MAC layer header that bumps the size up=
=0A=
to greater than 64K.=0A=
--> This can happen if the driver does not set the TSO sizing paramet=
ers=0A=
quite correctly, among other things.=0A=
=0A=
2 - TSO does work correctly, but results in different timing of the TCP=0A=
segments transmitted for the segment compared with non-TSO.=0A=
=0A=
I believe that, for otis@, disabling TSO reduced the frequency of Linux=0A=
client hangs, but did not stop them.=0A=
--> reverting the patch in r367492 (this patch is not in FreeBSD12) has=0A=
fixed the problem for him.=0A=
=0A=
rick=0A=
=0A=
--=0A=
Chris=0A=
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