netdev - Re: UDP "accept" proposed

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Date:	Tue, 18 Jun 2013 12:41:04 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	James Yonan <james@...nvpn.net>, netdev@...r.kernel.org
Subject: Re: UDP "accept" proposed

On 06/18/2013 12:17 PM, Eric Dumazet wrote:
> On Tue, 2013-06-18 at 11:52 +0200, Daniel Borkmann wrote:
>> On 06/18/2013 10:48 AM, James Yonan wrote:
>> [...]
>>> This is a disaster from a performance perspective because you can't take a UDP server that
>>   > binds to a single port and efficiently scale it up across multiple threads or processors
>>   > because you must operate off a single socket.
>
> Well not with current linux ;)
>
>>> But this would be a huge performance win for UDP servers (I'm thinking about OpenVPN in
>>   > particular) because making the kernel smarter about dispatching UDP datagrams would make it
>>   > much easier to develop scalable UDP servers on Linux.
>
>>
>> So SO_REUSEPORT that was added in 3.9 by Tom Herbert wouldn't
>> help in your case (+ f.e. steering flows to CPUs locally) ?
>>
>>     https://lwn.net/Articles/542629/
>
> Yes, but no need for particular steering.
>
> Incoming UDP message will match the 'connected socket' and will be
> delivered to the socket.
>
> RFS will then automatically do the right thing
>   ( Documentation/networking/scaling.txt )

+1, this was what I meant. I should have been more specific. ;-)

> Note that if you have a lot of sockets bound to the same port,
> this fix is needed :
>
> http://git.kernel.org/cgit/linux/kernel/git/davem/net.git/commit/?id=c87a124a5d5e8cf8e21c4363c3372bcaf53ea190
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