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.