Re: [PATCH] macvtap: Fix macvtap_get_queue to use rxhash first
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2011-11-24 09:59:03
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netdev
On Thu, Nov 24, 2011 at 01:47:14PM +0530, Krishna Kumar wrote:
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? 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 hunk ↗ jump to hunk
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]);