netdev - Re: "TCP: eth0: Driver has suspect GRO implementation, TCP performance may be compromised." message with "ethtool -K eth0 gro off"

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Message-ID: <20170324155619.GC23552@localhost.localdomain>
Date:   Fri, 24 Mar 2017 12:56:19 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Markus Trippelsdorf <markus@...ppelsdorf.de>,
        netdev@...r.kernel.org
Subject: Re: "TCP: eth0: Driver has suspect GRO implementation, TCP
 performance may be compromised." message with "ethtool -K eth0 gro off"

On Wed, Mar 22, 2017 at 06:47:42AM -0700, Eric Dumazet wrote:
> On Mon, 2017-03-20 at 16:27 -0300, Marcelo Ricardo Leitner wrote:
> >  This warning is a hint, and can not assume senders are not dumb.
> > 
> > Agreed. But we can make it consider such cases. What about the following
> > patch? (untested)
> > 
> > I think we can directly account for the size of the timestamps in there,
> > as that won't make a difference to congestion control in case it's
> > wrong, and also validate against MTU if we have it. I didn't subtract
> > the headers from MTU on purpose, as dealing with ipv4/ipv6 there is
> > not worth for the same reason.
> > 
> > This should silent this false-positive.
> 
> 
> Note that the problem could have its origin on a middle box,
> not on the host terminating the TCP flow.
> 
> So we can try hard, but we can't eliminate false positives.

Agreed both.

> 
> Maybe replace the 12 by MAX_TCP_OPTION_SPACE ?

Yes, can be. Thanks.

  Marcelo