Subject: Re: [PATCH V6 2/3] virtio-net: split out clean affinity function

From: Wanlong Gao <[email-masked]>
Date: Fri, 25 Jan 2013 12:20:16 +0800

On 01/25/2013 11:28 AM, Jason Wang wrote:
> On 01/21/2013 07:25 PM, Wanlong Gao wrote:
>> Split out the clean affinity function to virtnet_clean_affinity().
>>
>> Cc: Rusty Russell <[email-masked]>
>> Cc: "Michael S. Tsirkin" <[email-masked]>
>> Cc: Jason Wang <[email-masked]>
>> Cc: Eric Dumazet <[email-masked]>
>> Cc: [email-masked]
>> Cc: [email-masked]
>> Signed-off-by: Wanlong Gao <[email-masked]>
>> ---
>> V5->V6: NEW
>>
>>  drivers/net/virtio_net.c | 67 +++++++++++++++++++++++++++---------------------
>>  1 file changed, 38 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 70cd957..1a35a8c 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1016,48 +1016,57 @@ static int virtnet_vlan_rx_kill_vid(struct net_device *dev, u16 vid)
>>  	return 0;
>>  }
>>  
>> -static void virtnet_set_affinity(struct virtnet_info *vi, bool set)
>> +static void virtnet_clean_affinity(struct virtnet_info *vi, long hcpu)
>>  {
>>  	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
>> -	 * setting the affinity hint to eliminate the contention.
>> -	 */
>> -	if ((vi->curr_queue_pairs == 1 ||
>> -	     vi->max_queue_pairs != num_online_cpus()) && set) {
>> -		if (vi->affinity_hint_set)
>> -			set = false;
>> -		else
>> -			return;
>> -	}
>> -
>> -	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++;
>> -		}
>> -
>> -		vi->affinity_hint_set = true;
>> -	} else {
>> -		for(i = 0; i < vi->max_queue_pairs; i++) {
>> +	if (vi->affinity_hint_set) {
>> +		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)
>> +		for_each_online_cpu(cpu) {
>> +			if (cpu == hcpu)
>> +				continue;
>>  			*per_cpu_ptr(vi->vq_index, cpu) =
>>  				++i % vi->curr_queue_pairs;
>> +		}
>>  
> 
> Some questions here:
> 
> - Did we need reset the affinity of the queue here like the this?
> 
> virtqueue_set_affinity(vi->sq[*per_cpu_ptr(vi->vq_index, hcpu)], -1);
> virtqueue_set_affinity(vi->rq[*per_cpu_ptr(vi->vq_index, hcpu)], -1);

I think no, we are going to unset the affinity of all the set queues,
include hcpu.

> 
> - Looks like we need also reset the percpu index when
> vi->affinity_hint_set is false.

Yes, follow this and the comment on [1/3].

> - Does this really need this reset? Consider we're going to reset the
> percpu in CPU_DEAD?

I think resetting when CPU_DOWN_PREPARE can avoid selecting the wrong queue
on the dying CPU.

Thanks,
Wanlong Gao

> 
> Thanks
>>  		vi->affinity_hint_set = false;
>>  	}
>>  }
>>  
>> +static void virtnet_set_affinity(struct virtnet_info *vi)
>> +{
>> +	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
>> +	 * setting the affinity hint to eliminate the contention.
>> +	 */
>> +	if (vi->curr_queue_pairs == 1 ||
>> +	    vi->max_queue_pairs != num_online_cpus()) {
>> +		if (vi->affinity_hint_set)
>> +			virtnet_clean_affinity(vi, -1);
>> +		else
>> +			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;
>> +		i++;
>> +	}
>> +
>> +	vi->affinity_hint_set = true;
>> +}
>> +
>>  static void virtnet_get_ringparam(struct net_device *dev,
>>  				struct ethtool_ringparam *ring)
>>  {
>> @@ -1105,7 +1114,7 @@ static int virtnet_set_channels(struct net_device *dev,
>>  		netif_set_real_num_rx_queues(dev, queue_pairs);
>>  
>>  		get_online_cpus();
>> -		virtnet_set_affinity(vi, true);
>> +		virtnet_set_affinity(vi);
>>  		put_online_cpus();
>>  	}
>>  
>> @@ -1274,7 +1283,7 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
>>  {
>>  	struct virtio_device *vdev = vi->vdev;
>>  
>> -	virtnet_set_affinity(vi, false);
>> +	virtnet_clean_affinity(vi, -1);
>>  
>>  	vdev->config->del_vqs(vdev);
>>  
>> @@ -1398,7 +1407,7 @@ static int init_vqs(struct virtnet_info *vi)
>>  		goto err_free;
>>  
>>  	get_online_cpus();
>> -	virtnet_set_affinity(vi, true);
>> +	virtnet_set_affinity(vi);
>>  	put_online_cpus();
>>  
>>  	return 0;
> 
>