Re: [dpdk-dev] [PATCH] vhost: return ready when at least 1 vring is configured

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Changpeng,

On 9/22/20 9:22 AM, Liu, Changpeng wrote:
> Hi Maxime,
> 
> The code you wrote still need to check nr_vring is 0 or not, see the extra 2 lines added below, then it can work with my tests for now, could you submit a patch to DPDK to apply the patch? Thanks.

Thanks! You are right.

I'll send the patch now including your fix.

> BTW, dpdk vhost library still has an issue, it's not related with commit d0fcc38f, the Guest driver may only kick 1 vring even it sends NUM_QUEUES with a bigger value,
> this is quite common in seabios, e.g: virtio_blk will only use 1 vring in seabios, this means the backend will never get started in BIOS.
>

If I understand correctly, this is not a regression but has always been
here?

We should work on fixing it anyway, but I'm not sure to have the time
for v20.11.0. It would be great if you could provide steps to reproduce
it. Maybe file a bug in DPDK tracker?

Thanks,
Maxime

>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Monday, September 21, 2020 6:20 PM
>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
>> Cc: matan@mellanox.com; Xia, Chenbo <chenbo.xia@intel.com>; Zawadzki,
>> Tomasz <tomasz.zawadzki@intel.com>
>> Subject: Re: [PATCH] vhost: return ready when at least 1 vring is configured
>>
>>
>>
>> On 9/21/20 7:03 AM, Liu, Changpeng wrote:
>>> Hi Maxime,
>>>
>>>> -----Original Message-----
>>>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>>>> Sent: Friday, September 18, 2020 5:54 PM
>>>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
>>>> Cc: matan@mellanox.com; Xia, Chenbo <chenbo.xia@intel.com>; Zawadzki,
>>>> Tomasz <tomasz.zawadzki@intel.com>
>>>> Subject: Re: [PATCH] vhost: return ready when at least 1 vring is configured
>>>>
>>>> Hi Changpeng,
>>>>
>>>> On 9/1/20 9:07 AM, Changpeng Liu wrote:
>>>>> Commit d0fcc38f "vhost: improve device readiness notifications"
>>>>> needs at least 2 vrings before changing the device state to
>>>>> ready, this is fine for NET device but not correct for BLK
>>>>> device.
>>>>>
>>>>> The number of vring required should be based on the device
>>>>> type, e.g. virtio_scsi device needs at least 3 vrings, and
>>>>> virtio_net needs at least 2 vrings, virtio_blk needs at least
>>>>> 1 vring. So instead of doing it in vhost library it's better
>>>>> that the application who uses this library do this check.
>>>>>
>>>>> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
>>>>> ---
>>>>>  lib/librte_vhost/vhost_user.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>>>>> index c3c924f..4d1883c 100644
>>>>> --- a/lib/librte_vhost/vhost_user.c
>>>>> +++ b/lib/librte_vhost/vhost_user.c
>>>>> @@ -1343,7 +1343,7 @@
>>>>>  	       vq->enabled;
>>>>>  }
>>>>>
>>>>> -#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 2u
>>>>> +#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 1u
>>>>
>>>> I think it would be better to rely on VIRTIO_DEV_BUILTIN_VIRTIO_NET to
>>>> know whether it should wait for 1 or 2 queues to determine if ready.
>>> virtio_scsi needs at least 3 vrings, so both 1 and 2 can't work for virtio_scsi
>> device.
>>> Can we expose an API to let the caller to set the minimum number of vrings
>> required by
>>> virtio device?
>>
>> OK, thanks for pointing this out, I missed it.
>>
>> I'm not in favor of introducing an new API for this.
>> I propose to restrict change introduced in commit d0fcc38f to the
>> builtin net backend. Can you have a try with below patch?
>>
>> Thanks in advance,
>> Maxime
>>
>>>>
>>>>
>>>>>  static int
>>>>>  virtio_is_ready(struct virtio_net *dev)
>>>>>
>>>
>>
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index 501218e192..f571ef93fc 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -1343,21 +1343,25 @@ vq_is_ready(struct virtio_net *dev, struct
>> vhost_virtqueue *vq)
>>                vq->enabled;
>>  }
>>
>> -#define VIRTIO_DEV_NUM_VQS_TO_BE_READY 2u
>> +#define VIRTIO_BUILTIN_NUM_VQS_TO_BE_READY 2u
>>
>>  static int
>>  virtio_is_ready(struct virtio_net *dev)
>>  {
>>         struct vhost_virtqueue *vq;
>> -       uint32_t i;
>> +       uint32_t i, nr_vring = dev->nr_vring;
>>
>>         if (dev->flags & VIRTIO_DEV_READY)
>>                 return 1;
>>
>> -       if (dev->nr_vring < VIRTIO_DEV_NUM_VQS_TO_BE_READY)
>> -               return 0;
>> +       if (dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET) {
>> +               nr_vring = VIRTIO_BUILTIN_NUM_VQS_TO_BE_READY;
>> +
>> +               if (dev->nr_vring < nr_vring)
>> +                       return 0;
>> +       }
> 
>    +         if(!nr_vring)
>    +             return 0;
>>
>> -       for (i = 0; i < VIRTIO_DEV_NUM_VQS_TO_BE_READY; i++) {
>> +       for (i = 0; i < nr_vring; i++) {
>>                 vq = dev->virtqueue[i];
>>
>>                 if (!vq_is_ready(dev, vq))
>