netdev - Re: [PATCH net] net: reset ct before calling ndo_start

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Message-ID: <1485272563.16328.299.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 24 Jan 2017 07:42:43 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net] net: reset ct before calling ndo_start_xmit

On Tue, 2017-01-24 at 16:04 +0100, Paolo Abeni wrote:

> Double checking to see if I understood the above correctly: do you
> suggest to call nf_reset() from the affected drivers's
> ndo_features_check(), eventually adding such ndo if needed ?
> 
> I think calling nf_reset() in the common code should be better: the
> conntrack entry is hot in the cache and we may want to clear it early
> for as many devices as possible.

This would add a conditional test, which will be not correctly predicted
by CPU in tunnel or bonding/team very common cases.

While doing it in an affected driver would not penalize fast path.

A little bit harder sure, but performance matters ;)