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

Maxime Coquelin maxime.coquelin at redhat.com
Tue Sep 29 16:05:37 CEST 2020


Hi Fan,

The patch is already merged in main branch:

commit 09424c3f74311555c33d3d4cdc2ca3654ce13b1c
Author: Maxime Coquelin <maxime.coquelin at redhat.com>
Date:   Wed Sep 23 11:49:02 2020 +0200

    vhost: fix external backends readiness

    Commit d0fcc38f5fa4 ("vhost: improve device readiness notifications")
    makes the assumption that every Virtio devices are considered
    ready for preocessing as soon as first queue pair is configured
    and enabled.

    While this is true for Virtio-net, it isn't for Virtio-scsi
    and Virtio-blk.

    This patch fixes this by only making this assumption for
    the builtin Virtio-net backend, and restores back to previous
    behaviour for other backends.

    Fixes: d0fcc38f5fa4 ("vhost: improve device readiness notifications")

    Reported-by: Changpeng Liu <changpeng.liu at intel.com>
    Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
    Signed-off-by: Changpeng Liu <changpeng.liu at intel.com>
    Reviewed-by: Chenbo Xia <chenbo.xia at intel.com>


Regards,
Maxime

On 9/29/20 3:54 PM, Zhang, Roy Fan wrote:
> Hi Maxime,
> 
> Vhost-crypto has exactly the same issue. Changpeng's patch fixed it.
> Could you give me a shout when your patch is out, so I can have a test?
> 
> Regards,
> Fan
> 
>> -----Original Message-----
>> From: dev <dev-bounces at dpdk.org> On Behalf Of Maxime Coquelin
>> Sent: Wednesday, September 23, 2020 9:05 AM
>> To: Liu, Changpeng <changpeng.liu at intel.com>; dev at dpdk.org
>> Cc: matan at mellanox.com; Xia, Chenbo <chenbo.xia at intel.com>; Zawadzki,
>> Tomasz <tomasz.zawadzki at intel.com>
>> Subject: Re: [dpdk-dev] [PATCH] vhost: return ready when at least 1 vring is
>> configured
>>
>> 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 at redhat.com>
>>>> Sent: Monday, September 21, 2020 6:20 PM
>>>> To: Liu, Changpeng <changpeng.liu at intel.com>; dev at dpdk.org
>>>> Cc: matan at mellanox.com; Xia, Chenbo <chenbo.xia at intel.com>;
>> Zawadzki,
>>>> Tomasz <tomasz.zawadzki at 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 at redhat.com>
>>>>>> Sent: Friday, September 18, 2020 5:54 PM
>>>>>> To: Liu, Changpeng <changpeng.liu at intel.com>; dev at dpdk.org
>>>>>> Cc: matan at mellanox.com; Xia, Chenbo <chenbo.xia at intel.com>;
>> Zawadzki,
>>>>>> Tomasz <tomasz.zawadzki at 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 at 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))
>>>
> 



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