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

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Message-ID: <1380748118.19002.125.camel@edumazet-glaptop.roam.corp.google.com>
Date:	Wed, 02 Oct 2013 14:08:38 -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 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.



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