netdev - Re: udp v6 early demux?

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Message-ID: <54DAC43C.2090101@gmail.com>
Date:	Tue, 10 Feb 2015 21:53:48 -0500
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: udp v6 early demux?

On 02/10/2015 12:32 PM, Eric Dumazet wrote:
> On Tue, 2015-02-10 at 12:14 -0500, Vlad Yasevich wrote:
>> Hi
>>
>> While testing udpv6 lockless path, I noticed that there is no
>> support for udpv6 early demux?  Is there a technical reason why,
>> or was this just something that got forgotten (kind of like
>> lockeless sendmsg)?
> 
> If you have a use case for connected UDP ipv6 flows with performance
> issues, then you might add early demux I guess.
> 
> IPv4 udp early demux has been a bit of a hack actually,
> as Shawn main usage was multicast AFAIK
> 
> 63c6f81cdde5 udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup
> 610438b74496 udp: ipv4: fix potential use after free in udp_v4_early_demux()
> f69b923a758f udp: fix a typo in __udp4_lib_mcast_demux_lookup
> 421b3885bf6d udp: ipv4: Add udp early demux
> 
> 

I was more wondering if we can avoid the route the lookup.  It may not always be
a connected a case.  If you have multiple senders and a single receiver on the
same subnet, avoiding the route lookup with early demux might help.

-vlad
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