netdev - [PATCH 2.6.25] - Fix transmit queue stop mechanism

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Message-ID: <20080313071330.10331.66058.stgit@speedy5>
Date:	Thu, 13 Mar 2008 00:13:30 -0700
From:	Divy Le Ray <divy@...lsio.com>
To:	jeff@...zik.org
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	swise@...ngridcomputing.com
Subject: [PATCH 2.6.25] - Fix transmit queue stop mechanism

From: Divy Le Ray <divy@...lsio.com>

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@...lsio.com>
---

 drivers/net/cxgb3/sge.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/net/cxgb3/sge.c b/drivers/net/cxgb3/sge.c
index 979f3fc..db58687 100644
--- 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;
--
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