netdev - Re: ixgbe RSS not working as expected with 8021q and bridging

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Date:	Fri, 12 Feb 2010 20:48:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eldon Koyle <esk-netdev@....cs.usu.edu>
Cc:	netdev@...r.kernel.org
Subject: Re: ixgbe RSS not working as expected with 8021q and bridging

Le vendredi 12 février 2010 à 12:03 -0700, Eldon Koyle a écrit :
> On  Feb 10 13:50-0700, Eldon Koyle wrote:
> <snip>
> > I am now trying 2.6.32.7 with the in-tree ixgbe driver.  I am still
> > seeing some unusual behavior when bridging VLAN interfaces.  It looks
> > like there is an off-by-one error in the mapping from rx queue to tx
> > queue (ie. packets are sent on <rx queue number>-1 instead of using the
> > same rx and tx queue number).
> > 
> > Any idea what might cause this?
> 
> Looking at the code, we are having difficulty finding the problem.  I
> think we did find an accounting error in the vlan code, though.
> 
> In net/8021q/vlan_dev.c:
> 
> static netdev_tx_t vlan_dev_hard_start_xmit(struct sk_buff *skb,
>                                             struct net_device *dev)
> {
>         int i = skb_get_queue_mapping(skb);
>         struct netdev_queue *txq = netdev_get_tx_queue(dev, i);      
> ...
>         if (likely(ret == NET_XMIT_SUCCESS)) {
>                 txq->tx_packets++;
>                 txq->tx_bytes += len;
>         } else
>                 txq->tx_dropped++;
> ...
> }
> 
> skb_get_queue_mapping returns skb->queue_mapping, which is rx_queue + 1
> or 0 for unset.
> 
> Does dev->_tx[0] have some special meaning, or is this wrong?
> 

All multi queue drivers do same thing than vlan_dev_hard_start_xmit()

TX path is supposed to go through dev_pick_tx() & skb_tx_hash(), maybe
bridging has a shortcut and need a fix, like we also do in pktgen (sorry
I wont be able to check this before few days)




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