netdev - Re: [net-next 2/3] udp: Add udp early demux

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Date:	Tue, 01 Oct 2013 13:52:49 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shawn Bohrer <sbohrer@...advisors.com>
Cc:	David Miller <davem@...emloft.net>, tomk@...advisors.com,
	netdev <netdev@...r.kernel.org>
Subject: Re: [net-next 2/3] udp: Add udp early demux

On Tue, 2013-10-01 at 14:33 -0500, Shawn Bohrer wrote:
> The removal of the routing cache introduced a performance regression for
> some UDP workloads since a dst lookup must be done for each packet.
> This change caches the dst per socket in a similar manner to what we do
> for TCP by implementing early_demux.
> 
> For UDP multicast we can only cache the dst if there is only one
> receiving socket on the host.  Since caching only works when there is
> one receiving socket we do the multicast socket lookup using RCU.

For unicast, we should find a matching socket for early demux only if
this is a connected socket.

Otherwise, forwarding setups will break.

You probably need to add a minimum score to __udp4_lib_lookup()



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