netdev - RE: [PATCH V2 2/7] tcp: use limited socket backlog

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Date:	Thu, 04 Mar 2010 07:00:31 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Zhu, Yi" <yi.zhu@...el.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	Patrick McHardy <kaber@...sh.net>
Subject: RE: [PATCH V2 2/7] tcp: use limited socket backlog

Le jeudi 04 mars 2010 à 13:21 +0800, Zhu, Yi a écrit :
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > Then its a separate bug. MD5 support added so many bugs its not even
> > funny.
> 
> > Existing bugs are not an excuse for adding new ones, we try the reverse.
> > No ?
> 
> Can you show me where sk_drops is used by TCP and what SNMP MIB value
> should I use for backlog dropping? TCP_MIB_INERRS doesn't seem correct.

sk_drop is not yet used by TCP, because when backlog processing is
performed, TCP state machine has much finer grain capabilities to show
why a packet is dropped. In our backlog drop, we dont examine details of
packet and drop it at a lower level.

Please add a new counter, say LINUX_MIB_TCPBACKLOGDROP :

3 added lines:
- one in "include/linux/snmp.h" to define the MIB name
- one to define its string
- one to perform the increment when actual drop occurs)

A good starting point would be to study recent commit
72032fdbcde8b333e65b3430e1bcb4358e2d6716 from Jamal
(xfrm: Introduce LINUX_MIB_XFRMFWDHDRERROR)

For sk_drop, just increment it and we can get it at generic sock level.

Thanks !


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