cxgb3: Fix transmit queue stop mechanism

The last change in the Tx queue stop mechanism opens a window
where the Tx queue might be stopped after pending credits
returned.

Tx credits are returned via a control message generated by the HW.
It returns tx credits on demand, triggered by a completion bit
set in selective transmit packet headers.

The current code can lead to the Tx queue stopped
with all pending credits returned, and the current frame
not triggering a credit return. The Tx queue will then never be
awaken.

The driver could alternatively request a completion for packets
that stop the queue. It's however safer at this point to go back
to the pre-existing behaviour.

Signed-off-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/net/cxgb3/sge.c b/drivers/net/cxgb3/sge.c
index 979f3fc..db58687 100644 (file)
--- a/drivers/net/cxgb3/sge.c
+++ b/drivers/net/cxgb3/sge.c
@@ -1107,9 +1107,15 @@ int t3_eth_xmit(struct sk_buff *skb, struct net_device *dev)
        }
 
        q->in_use += ndesc;
-       if (unlikely(credits - ndesc < q->stop_thres))
-               if (USE_GTS || !should_restart_tx(q))
-                       t3_stop_queue(dev, qs, q);
+       if (unlikely(credits - ndesc < q->stop_thres)) {
+               t3_stop_queue(dev, qs, q);
+
+               if (should_restart_tx(q) &&
+                   test_and_clear_bit(TXQ_ETH, &qs->txq_stopped)) {
+                       q->restarts++;
+                       netif_wake_queue(dev);
+               }
+       }
 
        gen = q->gen;
        q->unacked += ndesc;