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

From: Wanlong Gao <[email-masked]>
Date: Fri, 25 Jan 2013 13:40:11 +0800

On 01/25/2013 01:13 PM, Jason Wang wrote:
> On 01/25/2013 12:20 PM, Wanlong Gao wrote:
>> 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.
> 
> Didn't understand this. What does 'wrong queue' here mean? Looks like
> you didn't change the preferable queue of the dying CPU and just change
> all others.

How about setting the vq index to -1 on hcpu when doing DOWN_PREPARE?
So that let it select txq to 0 when the CPU is dying.

Thanks,
Wanlong Gao

>>
>> 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;
>>>
> 
>