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

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Message-ID: <20131002212436.GC7824@sbohrermbp13-local.rgmadvisors.com>
Date:	Wed, 2 Oct 2013 16:24:36 -0500
From:	Shawn Bohrer <sbohrer@...advisors.com>
To:	Eric Dumazet <eric.dumazet@...il.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 Wed, Oct 02, 2013 at 02:08:38PM -0700, Eric Dumazet wrote:
> On Wed, 2013-10-02 at 15:35 -0500, Shawn Bohrer wrote:
> 
> > Sorry, I must be a little slow today.  I understand what you are
> > suggesting but I don't see how to implement it with a score.  Or at
> > least not without potentially changing existing behavior.  For example
> > I could make the inet->inet_daddr case add +100 to the score and I
> > would know that a score >= 100 was connected.  However, this would
> > unfairly favor that one case making a socket that only had a matching
> > inet_daddr be better than one that only had a matching inet_dport,
> > sk_bound_dev_if, and inet_rcv_saddr.
> > 
> 
> If early demux has to increment a socket refcount, then decrementing it
> because it found a non connected socket, this will be too expensive.
> 
> Also, keep in mind UDP chains can be long, so you should limit the early
> lookup to say a single socket.
> 
> TCP ehash is mostly empty (0 or 1 socket per bucket), so early demux
> really makes sense, but for UDP, there is no such property.

So... Are you suggesting that I just skip the early demux for unicast
UDP entirely?  That is fine by me since I only care about the
multicast case.

--
Shawn

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