netdev - Re: UDP multicast packet loss not reported if TX ring overrun?

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Message-ID: <4A940A10.60607@gmail.com>
Date:	Tue, 25 Aug 2009 17:58:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Sridhar Samudrala <sri@...ibm.com>,
	Nivedita Singhvi <niv@...ibm.com>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: UDP multicast packet loss not reported if TX ring overrun?

Christoph Lameter a écrit :
> On Tue, 25 Aug 2009, Eric Dumazet wrote:
> 
>> Christoph Lameter a ?crit :
>>> On Tue, 25 Aug 2009, Eric Dumazet wrote:
>>>
>>>> Please hold on, I would like to fully understand what's happening,
>>>> and test the patch :)
>>> Ok. It would be good if the drops would also be somehow noted by the UDP
>>> subsystem (one should see something with netstat -su) and may be even the
>>> socket. I see a drops column in /proc/net/udp. rx_drops, tx_drops?
>> This /proc/net/udp column is for rx_drops currently and was recently added...
> 
> So lets rename it to rx_drops and then add tx_drops?
> 

It wont be very nice, because it'll add yet another 32bits counter in each socket
structure, for a unlikely use. While rx_drops can happen if application is slow.

Also, tx_drops might be done later and not noticed.

Please read this old (and usefull) thread, with Alexey words...

http://oss.sgi.com/archives/netdev/2002-10/msg00612.html

http://oss.sgi.com/archives/netdev/2002-10/msg00617.html


So I bet your best choice is to set IP_RECVERR, as mentioned in 2002 by Jamal and Alexey :)
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