netdev - Re: pktgen and spin_lock

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Date:	Tue, 20 Oct 2009 14:10:13 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	NetDev <netdev@...r.kernel.org>, robert@...julf.net,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: pktgen and spin_lock_bh in xmit path

On 10/20/2009 11:54 AM, Eric Dumazet wrote:

> -	queue_map = skb_get_queue_mapping(pkt_dev->skb);
> +	queue_map = pkt_dev->cur_queue_map;
> +	/*
> +	 * tells skb_tx_hash() to use this tx queue.
> +	 * We should reset skb->mapping before each xmit() because
> +	 * xmit() might change it.
> +	 */
> +	skb_record_rx_queue(pkt_dev->skb, queue_map);
>   	txq = netdev_get_tx_queue(odev, queue_map);

I think that must be wrong.  The record_rx_queue sets it to queue_map + 1,
but the hard-start-xmit method (in ixgbe/ixgbe_main.c, at least), takes the
skb->queue_map and uses it as an index with no subtraction.

This causes watchdog timeouts because we are calling txq_trans_update in pktgen on
queue 0, for instance, but sending pkts on queue 1.  If queue 1 is ever
busy when the WD fires, link is reset.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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