netdev - Re: RX/dropped counter values for tagged packets

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Date:	Sat, 30 Mar 2013 22:44:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ani Sinha <ani@...stanetworks.com>
Cc:	netdev@...r.kernel.org, linuxdev@...rban.org
Subject: Re: RX/dropped counter values for tagged packets

On Sat, 2013-03-30 at 20:30 -0700, Ani Sinha wrote:

> On Sun, Mar 24, 2013 at 9:43 PM, Ani Sinha <ani@...stanetworks.com> wrote:
> > hello everyone :
> >
> > Please bear with me if you think I said something wrong.
> >
> > I was looking at the netif_receive_skb() code and it seems to me that
> > for vlan tagged packets, the counters are manipulated at two different
> > places. One is from vlan_do_receive() where the receive counters are
> > incremented. The other counter (the dropped counter) is incremented at
> > the very end of netif_receive_skb() when there are no takers for this
> > packet. The dropped counts are incremented for skb->dev->rx_dropped
> > whereas the receive counts are incremented for the vlan device
> > specific private stat counter values. When the numbers are reported on
> > /proc/net/dev (from where ifconfig gets the numbers), these two stat
> > counters are combined together (see dev_get_stats() where rx_dropped
> > is added to the device private stat numbers). So if no one is
> > receiving the tagged packets, it will be reported both as received and
> > dropped! I wonder whether I am analyzing it wrong or whether no one
> > has noticed this before or whether this is intentional.
> >
> > Any  clarification will be greatly appreciated. Again, I could be
> > wrong looking at the code, so please bear with me.
> >

I don't know, I am not reading this code like you, I see no problem.

If vlan_do_receive() return true, we "goto another_round" to deliver the
packt to vlan device.

vlan_do_receive() doesn't deliver the packet at all. It only prepares
the "another_round"

So if packet is delivered to vlan, we don't increment rx_dropped.

Just try by yourself, it is fine.



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