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Date: Fri, 25 Jan 2013 13:13:01 +0800
From: Jason Wang <jasowang@...hat.com>
To: gaowanlong@...fujitsu.com
CC: linux-kernel@...r.kernel.org,
Rusty Russell <rusty@...tcorp.com.au>,
"Michael S. Tsirkin" <mst@...hat.com>,
Eric Dumazet <erdnetdev@...il.com>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH V6 2/3] virtio-net: split out clean affinity function
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 <rusty@...tcorp.com.au>
>>> Cc: "Michael S. Tsirkin" <mst@...hat.com>
>>> Cc: Jason Wang <jasowang@...hat.com>
>>> Cc: Eric Dumazet <erdnetdev@...il.com>
>>> Cc: virtualization@...ts.linux-foundation.org
>>> Cc: netdev@...r.kernel.org
>>> Signed-off-by: Wanlong Gao <gaowanlong@...fujitsu.com>
>>> ---
>>> 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.
>
> 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;
>>
--
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