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Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_st
From: |
Longpeng (Mike) |
Subject: |
Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start |
Date: |
Thu, 16 Nov 2017 13:53:28 +0800 |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20120327 Thunderbird/11.0.1 |
Hi Jason & Michael,
Do you have any idea about this problem ?
--
Regards,
Longpeng(Mike)
On 2017/11/15 23:54, Longpeng(Mike) wrote:
> 2017-11-15 23:05 GMT+08:00 Jason Wang <address@hidden>:
>>
>>
>> On 2017年11月15日 22:55, Longpeng(Mike) wrote:
>>>
>>> Hi guys,
>>>
>>> We got a BUG report from our testers yesterday, the testing scenario was
>>> migrating a VM (Windows guest, *4 vcpus*, 4GB, vhost-user net: *7
>>> queues*).
>>>
>>> We found the cause reason, and we'll report the BUG or send a fix patch
>>> to upstream if necessary( we haven't test the upstream yet, sorry... ).
>>
>>
>> Could you explain this a little bit more?
>>
>>>
>>> We want to know why the vhost_net_start() must start *total queues* ( in
>>> our
>>> VM there're 7 queues ) but not *the queues that current used* ( in our VM,
>>> guest
>>> only uses the first 4 queues because it's limited by the number of vcpus)
>>> ?
>>>
>>> Looking forward to your help, thx :)
>>
>>
>> Since the codes have been there for years and works well for kernel
>> datapath. You should really explain what's wrong.
>>
>
> OK. :)
>
> In our scenario, the Windows's virtio-net driver only use the first 4
> queues and it
> *only set desc/avail/used table for the first 4 queues*, so in QEMU
> the desc/avail/
> used of the last 3 queues are ZERO, but unfortunately...
> '''
> vhost_net_start
> for (i = 0; i < total_queues; i++)
> vhost_net_start_one
> vhost_dev_start
> vhost_virtqueue_start
> '''
> In vhost_virtqueue_start(), it will calculate the HVA of
> desc/avail/used table, so for last
> 3 queues, it will use ZERO as the GPA to calculate the HVA, and then
> send the results
> to the user-mode backend ( we use *vhost-user* ) by
> vhost_virtqueue_set_addr().
>
> When the EVS get these address, it will update a *idx* which will be
> treated as vq's
> last_avail_idx when virtio-net stop ( pls see vhost_virtqueue_stop() ).
>
> So we get the following result after virtio-net stop:
> the desc/avail/used of the last 3 queues's vqs are all ZERO, but these vqs's
> last_avail_idx is NOT ZERO.
>
> At last, virtio_load() reports an error:
> '''
> if (!vdev->vq[i].vring.desc && vdev->vq[i].last_avail_idx) { // <--
> will be TRUE
> error_report("VQ %d address 0x0 "
> "inconsistent with Host index 0x%x",
> i, vdev->vq[i].last_avail_idx);
> return -1;
> }
> '''
>
> BTW, the problem won't appear if use Linux guest, because the Linux virtio-net
> driver will set all 7 queues's desc/avail/used tables. And the problem
> won't appear
> if the VM use vhost-net, because vhost-net won't update *idx* in SET_ADDR
> ioctl.
>
> Sorry for my pool English, Maybe I could describe the problem in Chinese for
> you
> in private if necessary.
>
>
>> Thanks
>
>
--
Regards,
Longpeng(Mike)
- [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Longpeng(Mike), 2017/11/15
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/15
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Longpeng(Mike), 2017/11/15
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Gonglei (Arei), 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Longpeng (Mike), 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Longpeng (Mike), 2017/11/16
- Re: [Qemu-devel] [Question] why need to start all queues in vhost_net_start, Jason Wang, 2017/11/16