netdev - Re: [PATCH net-next] tcp: Change txhash on some non-RTO retransmits

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Message-ID: <1476285744.5650.4.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Wed, 12 Oct 2016 17:22:24 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Lawrence Brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: Change txhash on some non-RTO retransmits

On Tue, 2016-10-11 at 20:56 -0700, Yuchung Cheng wrote:

> I thought more about this patch on my way home and have more
> questions: why do we exclude RTO retransmission specifically? also
> when we rehash, we'll introduce reordering either in recovery or after
> recovery, as some TCP CC like bbr would continue sending regardlessly,
> so starting in tcp_ack() with tp->txhash_want does not really prevent
> causing more reordering.

Note that changing txhash during a non rto retransmit is going to break
pacing on a bonding setup, since the change in txhash will likely select
a different slave, where MQ+FQ are the qdisc in place.