RE: Submission #3 for S2io 10GbE driver

["Feldman, Scott" <scott.feldman@xxxxxxxxx>]

> This is incorrect, and definitely an issue that needs to be addressed.
> 
> As I said, the model is, the driver calls netif_stop_queue() after 
> queueing a packet, when it knows there is no more room for a full 
> packet.  The tg3 driver does it like this:
>       
>       ...queue an skb to hardware...
>          if (TX_BUFFS_AVAIL(tp) <= (MAX_SKB_FRAGS + 1))
>                  netif_stop_queue(dev);
> 
> Therefore you guarantee the queue is stopped until you are 
> 100% certain that another skb (up to MAX_SKB_FRAGS + "main frag"
> fragments) may be queued to hardware.
> 
> You do -not- want to figure out "after the fact" that you 
> cannot queue the skb you were just passed.

But tg3 checks this case also and returns 1:

        /* This is a hard error, log it. */
        if (unlikely(TX_BUFFS_AVAIL(tp) <= (skb_shinfo(skb)->nr_frags +
1))) {
                netif_stop_queue(dev);
                ...
                return 1;
        }

Does this code path happen?

Using tg3 for reference, can we say this is the ideal model?

dev->hard_start

        if(!space_avail)
                stop_queue
                return 1;

        queue skb

        if(!space_avail)
                stop_queue

        return 0;

tx_clean

        if(queue_stopped && space_avail)
                wake_queue

-scott