On Sun, 2017-03-19 at 13:14 +0100, Markus Trippelsdorf wrote: > On 2017.02.06 at 19:12 -0200, Marcelo Ricardo Leitner wrote: > > On Fri, Feb 03, 2017 at 06:47:33AM -0800, Eric Dumazet wrote: > > > On Fri, 2017-02-03 at 12:28 -0200, Marcelo Ricardo Leitner wrote: > > > > > > > Aren't you mixing the endpoints here? MSS is the largest amount of data > > > > that the peer can receive in a single segment, and not how much it will > > > > send. For the sending part, that depends on what the other peer > > > > announced, and we can have 2 different MSS in a single connection, one > > > > for each peer. > > > > > > > > If a peer later wants to send larger segments, it can, but it must > > > > respect the mss advertised by the other peer during handshake. > > > > > > > > > > I am not mixing endpoints, you are. > > > > > > If you need to be convinced, please grab : > > > https://patchwork.ozlabs.org/patch/723028/ > > > > > > And just watch "ss -temoi ..." > > > > I still don't get it, but I also hit the warning on my laptop, using > > iwlwifi. Not sure what I did in order to trigger it, it was by accident. > > After many weeks without any warning, I've hit the issue again today: > > TCP: eth0: Driver has suspect GRO implementation, TCP performance may be > compromised. rcv_mss:1448 advmss:1448 len:1460 >
It is very possible the sender suddenly forgot to use TCP timestamps. This warning is a hint, and can not assume senders are not dumb.
