netdev - Re: [PATCH vhost 22/23] vdpa/mlx5: Don't reset VQs more than necessary

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Date: Wed, 19 Jun 2024 18:14:45 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Saeed Mahameed <saeedm@...dia.com>, 
	Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, Si-Wei Liu <si-wei.liu@...cle.com>, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org, 
	Cosmin Ratiu <cratiu@...dia.com>
Subject: Re: [PATCH vhost 22/23] vdpa/mlx5: Don't reset VQs more than necessary

On Mon, Jun 17, 2024 at 5:09 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> The vdpa device can be reset many times in sequence without any
> significant state changes in between. Previously this was not a problem:
> VQs were torn down only on first reset. But after VQ pre-creation was
> introduced, each reset will delete and re-create the hardware VQs and
> their associated resources.
>
> To solve this problem, avoid resetting hardware VQs if the VQs are still
> in a blank state.
>
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Reviewed-by: Cosmin Ratiu <cratiu@...dia.com>

Acked-by: Eugenio Pérez <eperezma@...hat.com>

> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index d80d6b47da61..1a5ee0d2b47f 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -3134,18 +3134,41 @@ static void init_group_to_asid_map(struct mlx5_vdpa_dev *mvdev)
>                 mvdev->group2asid[i] = 0;
>  }
>
> +static bool needs_vqs_reset(const struct mlx5_vdpa_dev *mvdev)
> +{
> +       struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> +       struct mlx5_vdpa_virtqueue *mvq = &ndev->vqs[0];
> +
> +       if (mvdev->status & VIRTIO_CONFIG_S_DRIVER_OK)
> +               return true;
> +
> +       if (mvq->fw_state != MLX5_VIRTIO_NET_Q_OBJECT_STATE_INIT)
> +               return true;
> +
> +       return mvq->modified_fields & (
> +               MLX5_VIRTQ_MODIFY_MASK_STATE |
> +               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_ADDRS |
> +               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_AVAIL_IDX |
> +               MLX5_VIRTQ_MODIFY_MASK_VIRTIO_Q_USED_IDX
> +       );
> +}
> +
>  static int mlx5_vdpa_compat_reset(struct vdpa_device *vdev, u32 flags)
>  {
>         struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>         struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> +       bool vq_reset;
>
>         print_status(mvdev, 0, true);
>         mlx5_vdpa_info(mvdev, "performing device reset\n");
>
>         down_write(&ndev->reslock);
>         unregister_link_notifier(ndev);
> -       teardown_vq_resources(ndev);
> -       init_mvqs(ndev);
> +       vq_reset = needs_vqs_reset(mvdev);
> +       if (vq_reset) {
> +               teardown_vq_resources(ndev);
> +               init_mvqs(ndev);
> +       }
>
>         if (flags & VDPA_RESET_F_CLEAN_MAP)
>                 mlx5_vdpa_destroy_mr_resources(&ndev->mvdev);
> @@ -3165,7 +3188,8 @@ static int mlx5_vdpa_compat_reset(struct vdpa_device *vdev, u32 flags)
>                 if (mlx5_vdpa_create_dma_mr(mvdev))
>                         mlx5_vdpa_warn(mvdev, "create MR failed\n");
>         }
> -       setup_vq_resources(ndev, false);
> +       if (vq_reset)
> +               setup_vq_resources(ndev, false);
>         up_write(&ndev->reslock);
>
>         return 0;
>
> --
> 2.45.1
>