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

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Date:	Thu, 1 Mar 2012 15:25:53 +0100
From:	Erik Hugne <erik.hugne@...csson.com>
To:	"netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>
CC:	"rodrigo.moya@...labora.co.uk" <rodrigo.moya@...labora.co.uk>,
	"David.Laight@...LAB.COM" <David.Laight@...LAB.COM>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"javier@...labora.co.uk" <javier@...labora.co.uk>,
	"lennart@...ttering.net" <lennart@...ttering.net>,
	"kay.sievers@...y.org" <kay.sievers@...y.org>,
	"alban.crequy@...labora.co.uk" <alban.crequy@...labora.co.uk>,
	"bart.cerneels@...labora.co.uk" <bart.cerneels@...labora.co.uk>,
	"sjoerd.simons@...labora.co.uk" <sjoerd.simons@...labora.co.uk>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: Re: [PATCH 0/10] af_unix: add multicast and filtering features to
 AF_UNIX

Hi
Have you considered using TIPC instead?
It already provides multicast messaging with guaranteed ordering, and reliable delivery  (SOCK _RDM)

//E
 

--Original message---
Sender: "netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>
Sent time: Thu Mar 01 14:56:00 CET 2012
To: eric.dumazet@...il.com
Cc: rodrigo.moya@...labora.co.uk, David.Laight@...LAB.COM, 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 03/01/2012 01:59 PM, Eric Dumazet wrote:
> Le jeudi 01 mars 2012 à 13:50 +0100, Rodrigo Moya a écrit :
>> the main problem in D-Bus we are trying to solve is the context
>> switches, since right now, there is a daemon, which listens on a UNIX
>> socket, and all traffic in the bus goes through it, and then the daemon
>> has to route the messages it gets on that socket to the corresponding
>> place(s). So, every time someone sends a message to D-Bus, since all
>> traffic goes through the daemon, dbus-daemon gets waked-up, which is one
>> of the biggest bottlenecks we are trying to fix.
>> 
>> That's why we are thinking about using multicast with socket filters, so
>> that the daemon only gets traffic it cares about and thus is not waked
>> up and context switches don't happen when not needed.
>> 
>> Using message queues, AFAICS, we would have the same problem, as the
>> daemon would create the message queue and would get all traffic, right?
>> 
> 
> This is why I mentioned extensions.


> 
> Anyway, if you think multicast sockets is the way to go, then you could
> setup a virtual network just to be able to use AF_INET multicast.
> 
> Thats probably doable without kernel patching.
> 

We could use AF_INET multicast on a local machine but we need some
ordering and control flow requirements that are not guaranteed on UDP
multicast over IP. That's why we thought to add a new address family
AF_MCAST.

To make it a general local multicast solution and not being too specific
we added some flags to control its behavior like
MCAST_MREQ_DROP_WHEN_FULL to decide to either block the sender or drop
the packet when one receiver has its queue full.

Regards,
Javier
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