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Date: Fri, 27 Sep 2013 17:35:29 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...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 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?
> ---
> 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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