netdev - Re: [PATCH] neigh: replace unres_qlen by unres_qlen

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Date:	Wed, 09 Nov 2011 08:55:25 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] neigh: replace unres_qlen by unres_qlen_bytes

Le mercredi 09 novembre 2011 à 00:18 -0500, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 09 Nov 2011 01:14:16 +0100
> 
> > unres_qlen is the number of frames we are able to queue per unresolved
> > neighbour. Its default value (3) was never changed and is responsible
> > for strange drops, especially if IP fragments are used, or multiple
> > sessions start in parallel. TCP initial congestion window is now bigger
> > than 3.
> 
> BTW, it has been observed in practice that if a long living connection
> suddently sends a burst of traffic after a very long idle period
> (hitting ARP expiry) or something invalidates the ARP entry in use, we
> will drop frames.  Because even if the ARP reply comes "fast" it's
> never quick enough to beat the burst of frames.
> 
> And if this happens in a scenerio where such lost packets potentially
> mean lost money...

I'll submit a more complete patch, including a fallback support of
unres_qlen, and one missing initializer in nl_ntbl_parm_policy[]

+	[NDTPA_QUEUE_LENBYTES]          = { .type = NLA_U32 },

 


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