netdev - Re: [PATCH] ipv4: Add sysctl knob to control early socket demux

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Date:	Sat, 23 Jun 2012 07:45:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	alexander.h.duyck@...el.com, netdev@...r.kernel.org,
	jeffrey.t.kirsher@...el.com, edumazet@...gle.com
Subject: Re: [PATCH] ipv4: Add sysctl knob to control early socket demux

On Fri, 2012-06-22 at 17:15 -0700, David Miller wrote:

> I applied this for now, making a minor change to move the local
> variables down into the new basic block you created.
> 

Hmm, sorry to come late, but you left NET_IPV4_EARLY_DEMUX=126 sysctl,
while this is deprecated way...

> There has got to be a way to make this really cheap.  At the very
> least we can have the GRO code store away the ports and therefore
> allow us to just do a direct call to try and demux the socket.  Thus,
> we'd avoid all of pskb_may_pull() et al. packet validations, and
> packet header pointer calculations.
> 
> Furthermore, we can reduce to overhead by making a special inet
> established hash demux that doesn't check for time-wait sockets,
> reducing the number of probes to 1 from 2.

The timewait hash chain is on the same cache line than established one.
And on a router, both chains are empty with a 99.999 % probability.


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