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

["Zhang, Roy Fan" <roy.fan.zhang@intel.com>]

Hi Maxime,

Thanks for telling me that but vhost_crypto is still breaking.

Virtio-crypto (both LKCF virtio-crypt driver and DPDK virtio-crypto PMD) won't create device queue until the crypto session is required to be created. Thus vq_is_ready() will never return true during initialization - hence new_device() in vhost_crypto sample app will never be triggered. Also since rte_vhost_driver_set_features() is called inside rte_vhost_crypto_create(), which is triggered by new_device() handler, we cannot update the dev->flags to bypass the "if (dev->flags & VIRTIO_DEV_BUILTIN_VIRTIO_NET)" check before new_device() is called.
what the new logic virtio_is_ready() requirement will never meet for vhost_crypto.

A way to fix it is with the following change - 

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index b00e1f91d..e5263a360 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1937,6 +1937,14 @@ vhost_user_set_vring_kick(struct virtio_net **pdev, struct VhostUserMsg *msg,
                }
        }
 
+       /* virtio-crypto vq is not ready until session is created. Check
+        * here if we need to initialize device again
+        */
+       if (!(dev->flags & VIRTIO_DEV_RUNNING)) {
+               if (dev->notify_ops->new_device(dev->vid) == 0)
+                       dev->flags |= VIRTIO_DEV_RUNNING;
+       }
+
        return RTE_VHOST_MSG_RESULT_OK;
 }

but I cannot add virtio_is_ready() inside the " if (!(dev->flags & VIRTIO_DEV_RUNNING))" check, since we need new_device() is called to set the feature flags - if to set the feature flags in the example instead, the logic will not right, since virtio-net does not require the user to set the flags themselves either.

Regards,
Fan


> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Tuesday, September 29, 2020 3:06 PM
> To: Zhang, Roy Fan <roy.fan.zhang@intel.com>; 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: [dpdk-dev] [PATCH] vhost: return ready when at least 1 vring is
> configured
> 
> Hi Fan,
> 
> The patch is already merged in main branch:
> 
> commit 09424c3f74311555c33d3d4cdc2ca3654ce13b1c
> Author: Maxime Coquelin <maxime.coquelin@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@intel.com>
>     Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>     Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
>     Reviewed-by: Chenbo Xia <chenbo.xia@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@dpdk.org> On Behalf Of Maxime Coquelin
> >> Sent: Wednesday, September 23, 2020 9:05 AM
> >> 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: [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@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))
> >>>
> >