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

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

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Wednesday, September 23, 2020 4:05 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 9/22/20 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?
Yes, I just found that recently, it already exists for a while.
> 
> 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?
No hurries , I can submit an issue tracker, it doesn't affect NET device and most of the storage scenarios.
> 
> 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))
> >