netdev - Re: [PATCH RFC 2/2] veth: propagate bridge GSO to peer

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Message-ID: <20171127201419.GA79@intel.com>
Date:   Mon, 27 Nov 2017 12:14:19 -0800
From:   Solio Sarabia <solio.sarabia@...el.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     dsahern@...il.com, davem@...emloft.net, netdev@...r.kernel.org,
        sthemmin@...rosoft.com
Subject: Re: [PATCH RFC 2/2] veth: propagate bridge GSO to peer

On Sun, Nov 26, 2017 at 11:07:25PM -0800, Stephen Hemminger wrote:
> On Sun, 26 Nov 2017 20:13:39 -0700
> David Ahern <dsahern@...il.com> wrote:
> 
> > On 11/26/17 11:17 AM, Stephen Hemminger wrote:
> > > This allows veth device in containers to see the GSO maximum
> > > settings of the actual device being used for output.
> > 
> > veth devices can be added to a VRF instead of a bridge, and I do not
> > believe the gso propagation works for L3 master devices.
> > 
> > From a quick grep, team devices do not appear to handle gso changes either.
> 
> This code should still work correctly, but no optimization would happen.
> The gso_max_size of the VRF or team will
> still be GSO_MAX_SIZE so there would be no change. If VRF or Team ever got smart
> enough to handle GSO limits, then the algorithm would handle it.

This patch propagates gso value from bridge to its veth endpoints.
However, since bridge is never aware of the GSO limit from underlying
interfaces, bridge/veth still have larger GSO size.

In the docker case, bridge is not linked directly to physical or
synthetic interfaces; it relies on iptables to decide which interface to
forward packets to.