linux-kernel - Re: [PATCH 0/10] af_unix: add multicast and filtering features to AF

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Message-ID: <CAAwP0s3Awu9-d5KDgBEdSrNmAJraL0JRO+Z6XVgYk6LX4djKyQ@mail.gmail.com>
Date:	Thu, 1 Mar 2012 20:02:04 +0100
From:	Javier Martinez Canillas <martinez.javier@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Luiz Augusto von Dentz <luiz.dentz@...il.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Rodrigo Moya <rodrigo.moya@...labora.co.uk>,
	David Laight <David.Laight@...lab.com>,
	David Miller <davem@...emloft.net>, javier@...labora.co.uk,
	lennart@...ttering.net, kay.sievers@...y.org,
	alban.crequy@...labora.co.uk, bart.cerneels@...labora.co.uk,
	sjoerd.simons@...labora.co.uk, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/10] af_unix: add multicast and filtering features to AF_UNIX

On Thu, Mar 1, 2012 at 6:59 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le 1 mars 2012 08:02, Luiz Augusto von Dentz <luiz.dentz@...il.com> a écrit :
>>
>> Contrary to someones believes I don't think AF_INET is that fast (e.g.
>> http://scottmoonen.com/2008/04/05/a-performance-comparison-of-af_unix-with-loopback-on-linux/)
>>
>
> Oh you mention a recent zork it seems ;)
>
> Are we speaking of performance problems, apart from scheduler problems
> for D-Bus (each message wakeing all receivers, all receivers read and
> drop message but the target) ?
>

Hi Eric,

The only performance problem we are talking about is the scheduling
for D-bus (context switch to the daemon for each message). With today
implementation the receivers only gets messages that were sent to it
but the D-bus daemon has to be wake it up for every message to he can
do the routing. For multicast messages (i.e: D-bus signals) this is
even worse since the daemon has to do a send() for each receiver.

> I am actually one of the few people working to improve performance on
> both AF_INET and AF_UNIX parts. Just take a look at recent commits.
>
> Right now you can send/receive millions of udp messages per second on
> your linux machine, if you figured out how to avoid process scheduler
> costs. If D-Bus wants more, I highly suggest using shared memory
> instead of passing messages.
> --

Yes, I also thought that AF_UNIX would be more efficient than AF_INET
but I was wrong. Yesterday I wrote some tests using our multicast unix
socket, UDP multicast over IP on a single machine and even multicast
using AF_NETLINK sockets and got very similar performance results.

The only problem is the ordering and control flow requirements for D-bus.

Best regards,
Javier
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