On 01/09/2013 09:52 AM, Wanlong Gao wrote:

On 01/08/2013 06:26 PM, Jason Wang wrote:

quoted

On 01/08/2013 06:07 PM, Wanlong Gao wrote:

quoted

As Michael mentioned, set affinity and select queue will not work very
well when CPU IDs are not consecutive, this can happen with hot unplug.
Fix this bug by traversal the online CPUs, and create a per cpu variable
to find the mapping from CPU to the preferable virtual-queue.

Cc: Rusty Russell <redacted>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Eric Dumazet <redacted>
Cc: virtualization@lists.linux-foundation.org
Cc: netdev@vger.kernel.org
Signed-off-by: Wanlong Gao <redacted>
---
 drivers/net/virtio_net.c | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a6fcf15..a77f86c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -41,6 +41,8 @@ module_param(gso, bool, 0444);
 #define VIRTNET_SEND_COMMAND_SG_MAX    2
 #define VIRTNET_DRIVER_VERSION "1.0.0"
 
+DEFINE_PER_CPU(int, vq_index) = -1;
+

I think this should not be a global one, consider we may have more than
one virtio-net cards with different max queues.

Yes, would you move this into virtio_info?

Yes, I think it's better.

quoted

quoted

 struct virtnet_stats {
 	struct u64_stats_sync tx_syncp;
 	struct u64_stats_sync rx_syncp;

@@ -1016,6 +1018,7 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev, u16 vid)
 static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
 {
 	int i;
+	int cpu;
 
 	/* In multiqueue mode, when the number of cpu is equal to the number of
 	 * queue pairs, we let the queue pairs to be private to one cpu by

@@ -1029,16 +1032,29 @@ static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
 			return;
 	}
 
-	for (i = 0; i < vi->max_queue_pairs; i++) {
-		int cpu = set ? i : -1;
-		virtqueue_set_affinity(vi->rq[i].vq, cpu);
-		virtqueue_set_affinity(vi->sq[i].vq, cpu);
-	}
+	if (set) {
+		i = 0;
+		for_each_online_cpu(cpu) {
+			virtqueue_set_affinity(vi->rq[i].vq, cpu);
+			virtqueue_set_affinity(vi->sq[i].vq, cpu);
+			per_cpu(vq_index, cpu) = i;
+			i++;
+			if (i >= vi->max_queue_pairs)
+				break;

Can this happen? we check only set when the number are equal.

will remove.

quoted

quoted

+		}
 
-	if (set)
 		vi->affinity_hint_set = true;
-	else
+	} else {
+		for(i = 0; i < vi->max_queue_pairs; i++) {
+			virtqueue_set_affinity(vi->rq[i].vq, -1);
+			virtqueue_set_affinity(vi->sq[i].vq, -1);
+		}
+
+		for_each_online_cpu(cpu)
+			per_cpu(vq_index, cpu) = -1;
+

This looks suboptimal since it may leads only txq zero is used.

So, which value is best for txq when we don't set affinity?
just remain to smp_processor_id()?

The value which will let us use all queues are ok.

How about this?
 
i = 0;
for_each_online_cpu(cpu)
    per_cpu(vq_index, cpu) = ++i % vi->curr_queues;

Thanks,
Wanlong Gao

quoted

quoted

 		vi->affinity_hint_set = false;
+	}
 }
 
 static void virtnet_get_ringparam(struct net_device *dev,

@@ -1127,12 +1143,15 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
 
 /* To avoid contending a lock hold by a vcpu who would exit to host, select the
  * txq based on the processor id.
- * TODO: handle cpu hotplug.
  */
 static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
 {
-	int txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) :
-		  smp_processor_id();
+	int txq = 0;
+
+	if (skb_rx_queue_recorded(skb))
+		txq = skb_get_rx_queue(skb);
+	else if ((txq = per_cpu(vq_index, smp_processor_id())) == -1)
+		txq = 0;
 
 	while (unlikely(txq >= dev->real_num_tx_queues))
 		txq -= dev->real_num_tx_queues;