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

["Liu, Changpeng" <changpeng.liu@intel.com>]

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.

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.

> -----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))