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

[David Gibson <david@gibson.dropbear.id.au>]

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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.

> I didn't really have time to debug this further.
> 
> At the moment I would be inclined to temporarily revert commit
> e63d281871ef ("tcp: leverage support of SO_PEEK_OFF socket option when
> available"), but it's not a good idea if this happens to be hiding some
> (unlikely?) issue with the flow table.
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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