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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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