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Date: Fri, 18 Jan 2013 14:25:22 +0800
From: Wanlong Gao <gaowanlong@...fujitsu.com>
To: Jason Wang <jasowang@...hat.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,
Wanlong Gao <gaowanlong@...fujitsu.com>
Subject: Re: [PATCH V5 1/2] virtio-net: fix the set affinity bug when CPU
IDs are not consecutive
On 01/18/2013 02:18 PM, Jason Wang wrote:
> On 01/18/2013 01:32 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>
>> ---
>> 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 | 60 +++++++++++++++++++++++++++++++++++++++---------
>> 1 file changed, 49 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index a6fcf15..440b0eb 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;
>> + }
>> }
>>
>> 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;
>> @@ -1248,7 +1274,9 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
>> {
>> struct virtio_device *vdev = vi->vdev;
>>
>> + get_online_cpus();
>> virtnet_set_affinity(vi, false);
>> + put_online_cpus();
>
> I think the {get|put}_online_cpus() is not necessary here when we are
> cleaning.
When cleaning, we also set the per-cpu variable, is avoiding hot plug
or unplug unnecessary?
Thanks,
Wanlong Gao
>>
>> vdev->config->del_vqs(vdev);
>>
>> @@ -1371,7 +1399,10 @@ 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 +1484,10 @@ 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 +1511,7 @@ 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 +1555,8 @@ 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 +1591,7 @@ 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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