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    SubjectRe: [PATCH 1/2] vdpa/mlx5: Avoid unnecessary query virtqueue
    On Tue, Feb 02, 2021 at 11:12:51AM +0800, Jason Wang wrote:
    >
    > On 2021/2/2 上午3:17, Si-Wei Liu wrote:
    > > On Mon, Feb 1, 2021 at 10:51 AM Si-Wei Liu <siwliu.kernel@gmail.com> wrote:
    > > > On Thu, Jan 28, 2021 at 5:46 AM Eli Cohen <elic@nvidia.com> wrote:
    > > > > suspend_vq should only suspend the VQ on not save the current available
    > > > > index. This is done when a change of map occurs when the driver calls
    > > > > save_channel_info().
    > > > Hmmm, suspend_vq() is also called by teardown_vq(), the latter of
    > > > which doesn't save the available index as save_channel_info() doesn't
    > > > get called in that path at all. How does it handle the case that
    > > > aget_vq_state() is called from userspace (e.g. QEMU) while the
    > > > hardware VQ object was torn down, but userspace still wants to access
    > > > the queue index?
    > > >
    > > > Refer to https://lore.kernel.org/netdev/1601583511-15138-1-git-send-email-si-wei.liu@oracle.com/
    > > >
    > > > vhost VQ 0 ring restore failed: -1: Resource temporarily unavailable (11)
    > > > vhost VQ 1 ring restore failed: -1: Resource temporarily unavailable (11)
    > > >
    > > > QEMU will complain with the above warning while VM is being rebooted
    > > > or shut down.
    > > >
    > > > Looks to me either the kernel driver should cover this requirement, or
    > > > the userspace has to bear the burden in saving the index and not call
    > > > into kernel if VQ is destroyed.
    > > Actually, the userspace doesn't have the insights whether virt queue
    > > will be destroyed if just changing the device status via set_status().
    > > Looking at other vdpa driver in tree i.e. ifcvf it doesn't behave like
    > > so. Hence this still looks to me to be Mellanox specifics and
    > > mlx5_vdpa implementation detail that shouldn't expose to userspace.
    >
    >
    > So I think we can simply drop this patch?
    >

    Yes, I agree. Let's just avoid it.

    > Thanks
    >
    >
    > > > -Siwei
    > > >
    > > >
    > > > > Signed-off-by: Eli Cohen <elic@nvidia.com>
    > > > > ---
    > > > > drivers/vdpa/mlx5/net/mlx5_vnet.c | 8 --------
    > > > > 1 file changed, 8 deletions(-)
    > > > >
    > > > > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > > > index 88dde3455bfd..549ded074ff3 100644
    > > > > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > > > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
    > > > > @@ -1148,8 +1148,6 @@ static int setup_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
    > > > >
    > > > > static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
    > > > > {
    > > > > - struct mlx5_virtq_attr attr;
    > > > > -
    > > > > if (!mvq->initialized)
    > > > > return;
    > > > >
    > > > > @@ -1158,12 +1156,6 @@ static void suspend_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *m
    > > > >
    > > > > if (modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_SUSPEND))
    > > > > mlx5_vdpa_warn(&ndev->mvdev, "modify to suspend failed\n");
    > > > > -
    > > > > - if (query_virtqueue(ndev, mvq, &attr)) {
    > > > > - mlx5_vdpa_warn(&ndev->mvdev, "failed to query virtqueue\n");
    > > > > - return;
    > > > > - }
    > > > > - mvq->avail_idx = attr.available_index;
    > > > > }
    > > > >
    > > > > static void suspend_vqs(struct mlx5_vdpa_net *ndev)
    > > > > --
    > > > > 2.29.2
    > > > >
    >

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