netdev - Re: Philosophical question: Is a UDP multicast datagram for which there is no socket match a drop or an ignore?

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Date:	Tue, 30 Sep 2014 16:23:18 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: Philosophical question:  Is a UDP multicast datagram for which
 there is no socket match a drop or an ignore?

On Tue, 2014-09-30 at 16:09 -0700, Rick Jones wrote:
> I've been looking at some additional perf <mutter> -e skb_kfree_skb 
> results, this time with a laptop connected to a corporate network with a 
> large number of Windows systems sending out what they are wont to 
> send...  The laptop is just sitting there no active netperfs or anything :)
> 
> I see profile hits for __udp4_lib_mcast_deliver() which has a 
> kfree_skb() call which will happen if either there were no sockets 
> found, or if an integral multiple of ARRAY_SIZE(stack) sockets are 
> found.  I'm assuming the latter is exceedingly rare.
> 
> Anywho, the philosophical question - is such a situation a drop 
> (indicating the existing kfree_skb()), or is it an ignore (indicating a 
> consume_skb())?  Should there be a statistic incremented for either of 
> those?

I guess we lack a UDP_MIB_NOPORTS increase here.


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