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Message-ID: <5102329B.4050806@cn.fujitsu.com>
Date: Fri, 25 Jan 2013 15:22:03 +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 03:04 PM, Jason Wang wrote:
> On 01/25/2013 02:42 PM, Wanlong Gao wrote:
>> On 01/25/2013 02:12 PM, Jason Wang wrote:
>>> 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@...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.
>>> 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?
>> IMHO, serialize every time will take lock and may slow down this path,
>> but the hot unplug path will be more cold than it. So I prefer reset the
>> preferable queues in DOWN_PREPARE but not serialize them. Agree?
>
> I think it's ok since we're in control path. And the point is when
> you're trying to reset the affinity / preferable queues during cpu
> hotplug callback, there will be another request in
> virtnet_set_channels() which changing the number of queues. So the the
> result of cpus == queues may out of date. Anyway you need some
> synchronization.
Agree, then I will add {get|put}_online_cpus to serialize this, thank you.
Regards,
Wanlong Gao
>
>>
>> Thanks,
>> Wanlong Gao
>>
>>> 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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