Re: [PATCH v2] tcp: probe for SO_PEEK_OFF both in tcpv4 and tcp6

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 24 Jul 2024 13:31:49 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Wed, Jul 24, 2024 at 10:40:15AM +1000, David Gibson wrote:
> > On Tue, Jul 23, 2024 at 10:29:36PM +0200, Stefano Brivio wrote:  
> > > On Tue, 23 Jul 2024 00:09:37 +0200
> > > Stefano Brivio <sbrivio@redhat.com> wrote:
> > >   
> > > > From: Jon Maloy <jmaloy@redhat.com>
> > > > 
> > > > Based on an original patch by Jon Maloy:
> > > >   
> > > 
> > > ...so, with this, the probing issue is solved: on a 6.10 kernel,
> > > SO_PEEK_OFF is not used, unless I disable IPv6 (with --ipv4-only / -4).
> > > 
> > > However, if I disable it, for some reason, resorting to IPv4, at least
> > > together with the flow table (applying just this patch to HEAD), I get
> > > something that looks like one of the "old" TCP stalls. On the host:
> > > 
> > >   $ ./passt -f -t 10000 -4
> > > 
> > > and in the guest:
> > > 
> > >   # ip link set dev eth0 up
> > >   # dhclient eth0
> > >   # iperf3 -s -p 10000
> > > 
> > > back to the host:
> > > 
> > >   $ iperf3 -c 127.0.0.1 -p 10000
> > >   Connecting to host 127.0.0.1, port 10000
> > >   [  5] local 127.0.0.1 port 39046 connected to 127.0.0.1 port 10000
> > >   [ ID] Interval           Transfer     Bitrate         Retr  Cwnd
> > >   [  5]   0.00-1.00   sec  11.2 MBytes  94.3 Mbits/sec    0   5.50 MBytes       
> > >   [  5]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec    0   5.50 MBytes       
> > >   [  5]   2.00-3.00   sec  0.00 Bytes  0.00 bits/sec    0   5.50 MBytes       
> > > 
> > > ...the transfer never recovers.  
> > 
> > Bother.  I've reproduced and am debugging now.  
> 
> Found it.  Looks like one of the cases where we need to set
> SO_PEEK_OFF was lost somewhere in the refactorings :(.

Hah, great, thanks, it fixes the issue on my setup as well. Re-running
all tests now...

-- 
Stefano