netdev - Re: [PATCH net-next v2 4/4] bonding: balance ICMP echoes in layer3+4 mode

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Message-ID: <CAGnkfhzEgaH1-YNWw1_HzB5FOhZHjKewLD9NP+rnTP21Htxnjw@mail.gmail.com>
Date:   Wed, 30 Oct 2019 00:03:38 +0100
From:   Matteo Croce <mcroce@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        netdev <netdev@...r.kernel.org>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller" <davem@...emloft.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Paul Blakey <paulb@...lanox.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 4/4] bonding: balance ICMP echoes in layer3+4 mode

On Tue, Oct 29, 2019 at 10:03 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 10/29/19 11:35 AM, Nikolay Aleksandrov wrote:
>
> > Hi Matteo,
> > Wouldn't it be more useful and simpler to use some field to choose the slave (override the hash
> > completely) in a deterministic way from user-space ?
> > For example the mark can be interpreted as a slave id in the bonding (should be
> > optional, to avoid breaking existing setups). ping already supports -m and
> > anything else can set it, this way it can be used to do monitoring for a specific
> > slave with any protocol and would be a much simpler change.
> > User-space can then implement any logic for the monitoring case and as a minor bonus
> > can monitor the slaves in parallel. And the opposite as well - if people don't want
> > these balanced for some reason, they wouldn't enable it.
> >
>
> I kind of agree giving user more control. But I do not believe we need to use the mark
> (this might be already used by other layers)
>
> TCP uses sk->sk_hash to feed skb->hash.
>
> Anything using skb_set_owner_w() is also using sk->sk_hash if set.
>
> So presumably we could add a generic SO_TXHASH socket option to let user space
> read/set this field.
>

Hi Eric,

this would work for locally generated echoes, but what about forwarded packets?
The point behind my changeset is to provide consistent results within
a session by using the same path for request and response,
but avoid all sessions flowing to the same path.
This should resemble what happens with TCP and UDP: different
connections, different port, probably a different path. And by doing
this in the flow dissector, other applications could benefit it.

Also, this should somewhat balance the traffic of a router forwarding
those packets. Maybe it's not so much in percentage, but in some
gateways be a considerable volume.

Regards,
-- 
Matteo Croce
per aspera ad upstream