netdev - Re: [PATCH] bonding: bond_select

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Date:	Thu, 17 Feb 2011 20:41:48 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Andy Gospodarek <andy@...yhouse.net>,
	Phil Oester <kernel@...uxace.com>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: bond_select_queue off by one

Phil Oester <kernel@...uxace.com> wrote:

>The bonding driver's bond_select_queue function simply returns
>skb->queue_mapping.  However queue_mapping could be == 16
>for queue #16.  This causes the following message to be flooded
>to syslog:
>
>kernel: bondx selects TX queue 16, but real number of TX queues is 16
>
>ndo_select_queue wants a zero-based number, so bonding driver needs
>to subtract one to return the proper queue number.  Also fix grammar in
>a comment while in the vicinity.

	Andy, can you comment on this?

	If memory serves, the omission of queue ID zero was on purpose;
is this patch going to break any of the functionality added by:

commit bb1d912323d5dd50e1079e389f4e964be14f0ae3
Author: Andy Gospodarek <andy@...yhouse.net>
Date:   Wed Jun 2 08:40:18 2010 +0000

    bonding: allow user-controlled output slave selection


Ben Hutchings <bhutchings@...arflare.com> wrote:

>This looks basically correct, but it should use the proper functions:
>
>	skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) : 0;

	As Ben points out, skb_rx_queue_recorded, skb_record_rx_queue,
et al, do the offset by one internally, but the bond_slave_override
function is comparing the slave's queue_id to the skb->queue_mapping.

	That makes me wonder if this patch is going to mess things up,
and if bond_slave_override should also use the skb_rx_queue_recorded, et
al, functions.

	-J

>Phil Oester
>
>Signed-off-by: Phil Oester <kernel@...uxace.com>
>
>
>--- linux-2.6/drivers/net/bonding/bond_main.c.orig	2011-01-30 09:15:09.813843817 -0800
>+++ linux-2.6/drivers/net/bonding/bond_main.c	2011-02-17 18:02:46.919050909 -0800
>@@ -4537,11 +4537,11 @@
> {
> 	/*
> 	 * This helper function exists to help dev_pick_tx get the correct
>-	 * destination queue.  Using a helper function skips the a call to
>+	 * destination queue.  Using a helper function skips a call to
> 	 * skb_tx_hash and will put the skbs in the queue we expect on their
> 	 * way down to the bonding driver.
> 	 */
>-	return skb->queue_mapping;
>+	return skb->queue_mapping ? skb->queue_mapping - 1 : 0;
> }
>
> static netdev_tx_t bond_start_xmit(struct sk_buff *skb, struct net_device *dev)

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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