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Date: Fri, 25 Jan 2013 17:11:22 +0800
From: Jason Wang <jasowang@...hat.com>
To: 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>,
"David S. Miller" <davem@...emloft.net>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH V7 1/3] virtio-net: fix the set affinity bug when CPU
IDs are not consecutive
On 01/25/2013 05:05 PM, Wanlong Gao wrote:
> On 01/25/2013 05:00 PM, Jason Wang wrote:
>> On 01/25/2013 04:36 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: "David S. Miller" <davem@...emloft.net>
>>> Cc: virtualization@...ts.linux-foundation.org
>>> Cc: netdev@...r.kernel.org
>>> Signed-off-by: Wanlong Gao <gaowanlong@...fujitsu.com>
>>> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>>> ---
>>> V6->V7:
>>> serialize virtnet_set_queues to avoid a race with cpu hotplug (Jason)
>>> 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..0f3afa8 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;
>>> + }
>>> }
>> Sorry, looks like the issue of v6 still exists, we need set per-cpu
>> index unconditionally here (and also in 2/3), the cpus != queues check
>> may bypass this setting.
> This fixed in 2/3, when cpus != queues, it will go into virtnet_clean_affinity(in 2/3),
> then vq index is set in virtnet_clean_affinity. Am I missing something?
Ah, so 2/3 looks fine. I suggest to fix this in 1/3 since it's not good
to introduce a bug in patch 1 and fix it in patch 2, and this can also
confuse the bisect.
Thanks
> Thanks,
> Wanlong Gao
>
>>>
>>> static void virtnet_get_ringparam(struct net_device *dev,
>>> @@ -1082,6 +1099,7 @@ static int virtnet_set_channels(struct net_device *dev,
>>> if (queue_pairs > vi->max_queue_pairs)
>>> return -EINVAL;
>>>
>>> + get_online_cpus();
>>> err = virtnet_set_queues(vi, queue_pairs);
>>> if (!err) {
>>> netif_set_real_num_tx_queues(dev, queue_pairs);
>>> @@ -1089,6 +1107,7 @@ static int virtnet_set_channels(struct net_device *dev,
>>>
>>> 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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