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Date: Sun, 29 Sep 2013 11:14:48 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH net-next] virtio-net: switch to use XPS to choose txq
On 09/27/2013 10:35 PM, Michael S. Tsirkin wrote:
> On Fri, Sep 27, 2013 at 01:57:24PM +0800, Jason Wang wrote:
>> We used to use a percpu structure vq_index to record the cpu to queue
>> mapping, this is suboptimal since it duplicates the work of XPS and
>> loses all other XPS functionality such as allowing use to configure
>> their own transmission steering strategy.
>>
>> So this patch switches to use XPS and suggest a default mapping when
>> the number of cpus is equal to the number of queues. With XPS support,
>> there's no need for keeping per-cpu vq_index and .ndo_select_queue(),
>> so they were removed also.
>>
>> Cc: Rusty Russell <rusty@...tcorp.com.au>
>> Cc: Michael S. Tsirkin <mst@...hat.com>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> More lines deleted that added is good :)
> But how does the result perform?
> About the same?
>
Yes, the same.
>> ---
>> drivers/net/virtio_net.c | 55 +++++++--------------------------------------
>> 1 files changed, 9 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index defec2b..4102c1b 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -127,9 +127,6 @@ 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;
>> -
>> /* CPU hot plug notifier */
>> struct notifier_block nb;
>> };
>> @@ -1063,7 +1060,6 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev,
>> static void virtnet_clean_affinity(struct virtnet_info *vi, long hcpu)
>> {
>> int i;
>> - int cpu;
>>
>> if (vi->affinity_hint_set) {
>> for (i = 0; i < vi->max_queue_pairs; i++) {
>> @@ -1073,20 +1069,11 @@ static void virtnet_clean_affinity(struct virtnet_info *vi, long hcpu)
>>
>> vi->affinity_hint_set = false;
>> }
>> -
>> - i = 0;
>> - for_each_online_cpu(cpu) {
>> - if (cpu == hcpu) {
>> - *per_cpu_ptr(vi->vq_index, cpu) = -1;
>> - } else {
>> - *per_cpu_ptr(vi->vq_index, cpu) =
>> - ++i % vi->curr_queue_pairs;
>> - }
>> - }
>> }
>>
>> static void virtnet_set_affinity(struct virtnet_info *vi)
>> {
>> + cpumask_var_t cpumask;
>> int i;
>> int cpu;
>>
>> @@ -1100,15 +1087,21 @@ static void virtnet_set_affinity(struct virtnet_info *vi)
>> return;
>> }
>>
>> + if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
>> + return;
>> +
>> 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;
>> + cpumask_clear(cpumask);
>> + cpumask_set_cpu(cpu, cpumask);
>> + netif_set_xps_queue(vi->dev, cpumask, i);
>> i++;
>> }
>>
>> vi->affinity_hint_set = true;
>> + free_cpumask_var(cpumask);
>> }
>>
>> static int virtnet_cpu_callback(struct notifier_block *nfb,
>> @@ -1217,28 +1210,6 @@ static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>> return 0;
>> }
>>
>> -/* To avoid contending a lock hold by a vcpu who would exit to host, select the
>> - * txq based on the processor id.
>> - */
>> -static u16 virtnet_select_queue(struct net_device *dev, struct sk_buff *skb)
>> -{
>> - 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;
>> -
>> - return txq;
>> -}
>> -
>> static const struct net_device_ops virtnet_netdev = {
>> .ndo_open = virtnet_open,
>> .ndo_stop = virtnet_close,
>> @@ -1250,7 +1221,6 @@ static const struct net_device_ops virtnet_netdev = {
>> .ndo_get_stats64 = virtnet_stats,
>> .ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>> .ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
>> - .ndo_select_queue = virtnet_select_queue,
>> #ifdef CONFIG_NET_POLL_CONTROLLER
>> .ndo_poll_controller = virtnet_netpoll,
>> #endif
>> @@ -1559,10 +1529,6 @@ 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);
>> @@ -1589,7 +1555,7 @@ 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_index;
>> + goto free_stats;
>>
>> netif_set_real_num_tx_queues(dev, 1);
>> netif_set_real_num_rx_queues(dev, 1);
>> @@ -1640,8 +1606,6 @@ 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:
>> @@ -1678,7 +1642,6 @@ 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);
>> }
>> --
>> 1.7.1
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