netdev - Re: [PATCH net-next 0/5] net: introduce noref sk

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Date:   Thu, 21 Sep 2017 11:42:11 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, pablo@...filter.org, fw@...len.de,
        edumazet@...gle.com, hannes@...essinduktion.org
Subject: Re: [PATCH net-next 0/5] net: introduce noref sk

Hi,

Thanks for the feedback!

On Wed, 2017-09-20 at 20:20 -0700, David Miller wrote:
> From: Paolo Abeni <pabeni@...hat.com>
> Date: Wed, 20 Sep 2017 18:54:00 +0200
> 
> > This series introduce the infrastructure to store inside the skb a socket
> > pointer without carrying a refcount to the socket.
> > 
> > Such infrastructure is then used in the network receive path - and
> > specifically the early demux operation.
> > 
> > This allows the UDP early demux to perform a full lookup for UDP sockets,
> > with many benefits:
> > 
> > - the UDP early demux code is now much simpler
> > - the early demux does not hit any performance penalties in case of UDP hash
> >   table collision - previously the early demux performed a partial, unsuccesful,
> >   lookup
> > - early demux is now operational also for unconnected sockets.
> > 
> > This infrastrcture will be used in follow-up series to allow dst caching for
> > unconnected UDP sockets, and than to extend the same features to TCP listening
> > sockets.
> 
> Like Eric, I find this series (while exciting) quite scary :-)
> 
> You really have to post some kind of performance numbers in your
> header posting in order to justify something with these ramifications
> and scale.

This is actually a preparatory work for the next series which will
bring in the real gain. The next patches are still to be polished so we
 posted this separately to get some early feedback. 

If that would help, I can post the follow-up soon as RFC. Overall -
with the follow-up appplied, too - when using a single rx ingress
queue, I measured ~20% tput gain for unconnected ipv4 sockets - with
rp_filter disabled - and ~30% for ipv6 sockets. In case of multiple
ingress queues, the gain is smaller but still measurable (roughly 5%). 

Please let me know if you prefer the see the full work early. 

Thanks,

Paolo