On Thu, Nov 24, 2011 at 06:13:41PM +0800, jasowang wrote:

On 11/24/2011 05:59 PM, Michael S. Tsirkin wrote:

quoted

On Thu, Nov 24, 2011 at 01:47:14PM +0530, Krishna Kumar wrote:

quoted

It was reported that the macvtap device selects a
different vhost (when used with multiqueue feature)
for incoming packets of a single connection. Use
packet hash first. Patch tested on MQ virtio_net.

So this is sure to address the problem, why exactly does this happen?

Ixgbe has flow director and bind queue to host cpu, so it can make
sure the packet of a flow to be handled by the same queue/cpu. So
when vhost thread moves from one host cpu to another, ixgbe would
therefore send the packet to the new cpu/queue.

Confused. How does ixgbe know about vhost thread moving?

quoted

Does your device spread a single flow across multiple RX queues? Would
not that cause trouble in the TCP layer?
It would seem that using the recorded queue should be faster with
less cache misses. Before we give up on that, I'd
like to understand why it's wrong. Do you know?

quoted

Signed-off-by: Krishna Kumar<redacted>
---
 drivers/net/macvtap.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff -ruNp org/drivers/net/macvtap.c new/drivers/net/macvtap.c

--- org/drivers/net/macvtap.c	2011-10-22 08:38:01.000000000 +0530
+++ new/drivers/net/macvtap.c	2011-11-16 18:34:51.000000000 +0530

@@ -175,6 +175,14 @@ static struct macvtap_queue *macvtap_get
 	if (!numvtaps)
 		goto out;

+	/* Check if we can use flow to select a queue */
+	rxq = skb_get_rxhash(skb);
+	if (rxq) {
+		tap = rcu_dereference(vlan->taps[rxq % numvtaps]);
+		if (tap)
+			goto out;
+	}
+
 	if (likely(skb_rx_queue_recorded(skb))) {
 		rxq = skb_get_rx_queue(skb);

@@ -186,14 +194,6 @@ static struct macvtap_queue *macvtap_get
 			goto out;
 	}

-	/* Check if we can use flow to select a queue */
-	rxq = skb_get_rxhash(skb);
-	if (rxq) {
-		tap = rcu_dereference(vlan->taps[rxq % numvtaps]);
-		if (tap)
-			goto out;
-	}
-
 	/* Everything failed - find first available queue */
 	for (rxq = 0; rxq<  MAX_MACVTAP_QUEUES; rxq++) {
 		tap = rcu_dereference(vlan->taps[rxq]);

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