On Sat, Jul 26, 2008 at 02:18:46AM -0700, David Miller wrote:
...

I think there might be an easier way, but we may have
to modify the state bits a little.

Every call into ->hard_start_xmit() is made like this:

1. lock TX queue
2. check TX queue stopped
3. call ->hard_start_xmit() if not stopped

This means that we can in fact do something like:

	unsigned int i;

	for (i = 0; i < dev->num_tx_queues; i++) {
		struct netdev_queue *txq;

		txq = netdev_get_tx_queue(dev, i);
		spin_lock_bh(&txq->_xmit_lock);
		netif_tx_freeze_queue(txq);
		spin_unlock_bh(&txq->_xmit_lock);
	}

netif_tx_freeze_queue() just sets a new bit we add.

Then we go to the ->hard_start_xmit() call sites and check this new
"frozen" bit as well as the existing "stopped" bit.

When we unfreeze each queue later, we see if it is stopped, and if not
we schedule it's qdisc for packet processing.

I guess some additional synchronization will be added yet to prevent
parallel freeze and especially unfreeze.

Jarek P.
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