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

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Message-Id: <20090828.122658.188210079.davem@davemloft.net>
Date:	Fri, 28 Aug 2009 12:26:58 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	cl@...ux-foundation.org
Cc:	eric.dumazet@...il.com, sri@...ibm.com, dlstevens@...ibm.com,
	netdev@...r.kernel.org, niv@...ux.vnet.ibm.com
Subject: Re: UDP multicast packet loss not reported if TX ring overrun?

From: Christoph Lameter <cl@...ux-foundation.org>
Date: Fri, 28 Aug 2009 12:15:39 -0400 (EDT)

> Because you need drop statistics on a device to figure out when you may
> want to increase the TX buffers for a device. If a packet was dropped
> because of a lack of TX buffers then we need to know.

Christoph, the qdisc layer is there and is where the drops occur, and
you therefore have to be aware of it.

I'm not accepting changes like the patch you propose here, it's not
the correct thing to do.

The device never saw the packet, it never dropped it.

The qdisc saw it, the qdisc dropped it, and therefore that's where we
account for it.
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