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SubjectRe: [PATCH V6 2/3] virtio-net: split out clean affinity function
On 01/25/2013 01:40 PM, Wanlong Gao wrote:
> 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 <rusty@rustcorp.com.au>
>>>>> Cc: "Michael S. Tsirkin" <mst@redhat.com>
>>>>> Cc: Jason Wang <jasowang@redhat.com>
>>>>> Cc: Eric Dumazet <erdnetdev@gmail.com>
>>>>> Cc: virtualization@lists.linux-foundation.org
>>>>> Cc: netdev@vger.kernel.org
>>>>> Signed-off-by: Wanlong Gao <gaowanlong@cn.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.
> 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.

Looks safe, so look like what you're going to solve here is the the race
between cpu hotplug and virtnet_set_channels(). A possible better
solution is to serialize them by protecting virtnet_set_queues() by
get_online_cpus() also. After this, we can make sure the number of
channels were not changed during cpu hotplug, and looks like there's no
need to reset the preferable queues in DOWN_PREPARE.

What's your opinion?

Thanks
>
> 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;
>>
> --
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