From: Shawn Bohrer <sbohrer@rgmadvisors.com>
Date: Mon, 7 Oct 2013 16:01:40 +0000 (-0500)
Subject: net: ipv4 only populate IP_PKTINFO when needed
X-Git-Tag: v3.13-rc1~105^2~213
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fbf8866d65d5de84f75563eb0edd7fc27dbe9a90;p=pandora-kernel.git

net: ipv4 only populate IP_PKTINFO when needed

The since the removal of the routing cache computing
fib_compute_spec_dst() does a fib_table lookup for each UDP multicast
packet received.  This has introduced a performance regression for some
UDP workloads.

This change skips populating the packet info for sockets that do not have
IP_PKTINFO set.

Benchmark results from a netperf UDP_RR test:
Before 89789.68 transactions/s
After  90587.62 transactions/s

Benchmark results from a fio 1 byte UDP multicast pingpong test
(Multicast one way unicast response):
Before 12.63us RTT
After  12.48us RTT

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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