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Date: Fri, 25 Jan 2013 13:40:11 +0800
From: Wanlong Gao <gaowanlong@...fujitsu.com>
To: Jason Wang <jasowang@...hat.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,
Wanlong Gao <gaowanlong@...fujitsu.com>
Subject: Re: [PATCH V6 2/3] virtio-net: split out clean affinity function
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@...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.
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;
>>>
>
>
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