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Message-ID: <5101FB65.4040805@redhat.com>
Date: Fri, 25 Jan 2013 11:26:29 +0800
From: Jason Wang <jasowang@...hat.com>
To: Wanlong Gao <gaowanlong@...fujitsu.com>
CC: linux-kernel@...r.kernel.org,
Rusty Russell <rusty@...tcorp.com.au>,
"Michael S. Tsirkin" <mst@...hat.com>,
Eric Dumazet <erdnetdev@...il.com>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH V6 1/3] virtio-net: fix the set affinity bug when CPU
IDs are not consecutive
On 01/21/2013 07:25 PM, Wanlong Gao wrote:
> 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 <rusty@...tcorp.com.au>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Cc: Eric Dumazet <erdnetdev@...il.com>
> Cc: virtualization@...ts.linux-foundation.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Wanlong Gao <gaowanlong@...fujitsu.com>
> ---
> V5->V6:
> remove {get|put}_online_cpus from virtnet_del_vqs (Jason)
> V4->V5:
> Add get/put_online_cpus to avoid CPUs go up and down during operations (Rusty)
>
> V3->V4:
> move vq_index into virtnet_info (Jason)
> change the mapping value when not setting affinity (Jason)
> address the comments about select_queue (Rusty)
>
> drivers/net/virtio_net.c | 58 +++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 47 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index a6fcf15..70cd957 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -123,6 +123,9 @@ struct virtnet_info {
>
> /* Does the affinity hint is set for virtqueues? */
> bool affinity_hint_set;
> +
> + /* Per-cpu variable to show the mapping from CPU to virtqueue */
> + int __percpu *vq_index;
> };
>
> struct skb_vnet_hdr {
> @@ -1016,6 +1019,7 @@ 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 +1033,29 @@ 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_ptr(vi->vq_index, cpu) = i;
> + i++;
> + }
>
> - 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);
> + }
> +
> + i = 0;
> + for_each_online_cpu(cpu)
> + *per_cpu_ptr(vi->vq_index, cpu) =
> + ++i % vi->curr_queue_pairs;
> +
> vi->affinity_hint_set = false;
> + }
> }
This looks wrong, since you always choose txq based on the per-cpu, I
think the per-cpu index should be set unconditionally even if cpus !=
queues. Consider you may boot a guest with 4 vcpus and 2 queues, you
need initialize it also in this case. Otherwise, you may always get txq
0 to be selected.
>
> static void virtnet_get_ringparam(struct net_device *dev,
> @@ -1087,7 +1104,9 @@ static int virtnet_set_channels(struct net_device *dev,
> netif_set_real_num_tx_queues(dev, queue_pairs);
> netif_set_real_num_rx_queues(dev, queue_pairs);
>
> + get_online_cpus();
> virtnet_set_affinity(vi, true);
> + put_online_cpus();
> }
>
> return err;
> @@ -1127,12 +1146,19 @@ 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;
> + struct virtnet_info *vi = netdev_priv(dev);
> +
> + if (skb_rx_queue_recorded(skb)) {
> + txq = skb_get_rx_queue(skb);
> + } else {
> + txq = *__this_cpu_ptr(vi->vq_index);
> + if (txq == -1)
> + txq = 0;
> + }
>
> while (unlikely(txq >= dev->real_num_tx_queues))
> txq -= dev->real_num_tx_queues;
> @@ -1371,7 +1397,10 @@ static int init_vqs(struct virtnet_info *vi)
> if (ret)
> goto err_free;
>
> + get_online_cpus();
> virtnet_set_affinity(vi, true);
> + put_online_cpus();
> +
> return 0;
>
> err_free:
> @@ -1453,6 +1482,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (vi->stats == NULL)
> goto free;
>
> + vi->vq_index = alloc_percpu(int);
> + if (vi->vq_index == NULL)
> + goto free_stats;
> +
> mutex_init(&vi->config_lock);
> vi->config_enable = true;
> INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> @@ -1476,7 +1509,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> /* Allocate/initialize the rx/tx queues, and invoke find_vqs */
> err = init_vqs(vi);
> if (err)
> - goto free_stats;
> + goto free_index;
>
> netif_set_real_num_tx_queues(dev, 1);
> netif_set_real_num_rx_queues(dev, 1);
> @@ -1520,6 +1553,8 @@ free_recv_bufs:
> free_vqs:
> cancel_delayed_work_sync(&vi->refill);
> virtnet_del_vqs(vi);
> +free_index:
> + free_percpu(vi->vq_index);
> free_stats:
> free_percpu(vi->stats);
> free:
> @@ -1554,6 +1589,7 @@ static void virtnet_remove(struct virtio_device *vdev)
>
> flush_work(&vi->config_work);
>
> + free_percpu(vi->vq_index);
> free_percpu(vi->stats);
> free_netdev(vi->dev);
> }
--
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