Re: [PATCH] e1000 - get rid of tx_lock

Stephen Hemminger [off-list ref] :

The e1000 driver has an tx_lock which unneeded.  It is only used to protect
the start/stop queue flags which are already handled by doing atomic bit
operations.

I am not terribly used to this code but as far as I can read it, the lock
avoids that the condition which leads to netif_stop_queue() in the xmit
thread changes (due to an irq) "just before" netif_stop_queue() is actually
called. 

So, if the lock is removed, I would be tempted to have the xmit thread
issue an smp_rmb() and revalidate that it was fine to netif_stop_queue().

Otherwise, one could have:

[e1000_xmit_frame]
	if (E1000_DESC_UNUSED(&adapter->tx_ring) < count + 2 ) {
	<- at the same time on a different CPU ->
	[...]
	e1000_clean_tx_irq::netif_wake_queue() // Plenty of room has been made
	[...]
	<- back to e1000_xmit_frame() ->
		netif_stop_queue
		return 1; 
	}


--
Ueimor