linux-kernel - Re: [PATCH vhost 20/23] vdpa/mlx5: Pre-create hardware VQs at vdpa .dev

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Date: Wed, 19 Jun 2024 17:54:09 +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 20/23] vdpa/mlx5: Pre-create hardware VQs at vdpa
 .dev_add time

On Mon, Jun 17, 2024 at 5:09 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> Currently, hardware VQs are created right when the vdpa device gets into
> DRIVER_OK state. That is easier because most of the VQ state is known by
> then.
>
> This patch switches to creating all VQs and their associated resources
> at device creation time. The motivation is to reduce the vdpa device
> live migration downtime by moving the expensive operation of creating
> all the hardware VQs and their associated resources out of downtime on
> the destination VM.
>
> The VQs are now created in a blank state. The VQ configuration will
> happen later, on DRIVER_OK. Then the configuration will be applied when
> the VQs are moved to the Ready state.
>
> When .set_vq_ready() is called on a VQ before DRIVER_OK, special care is
> needed: now that the VQ is already created a resume_vq() will be
> triggered too early when no mr has been configured yet. Skip calling
> resume_vq() in this case, let it be handled during DRIVER_OK.
>
> For virtio-vdpa, the device configuration is done earlier during
> .vdpa_dev_add() by vdpa_register_device(). Avoid calling
> setup_vq_resources() a second time in that case.
>

I guess this happens if virtio_vdpa is already loaded, but I cannot
see how this is different here. Apart from the IOTLB, what else does
it change from the mlx5_vdpa POV?

> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Reviewed-by: Cosmin Ratiu <cratiu@...dia.com>
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 37 ++++++++++++++++++++++++++++++++-----
>  1 file changed, 32 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 249b5afbe34a..b2836fd3d1dd 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -2444,7 +2444,7 @@ static void mlx5_vdpa_set_vq_ready(struct vdpa_device *vdev, u16 idx, bool ready
>         mvq = &ndev->vqs[idx];
>         if (!ready) {
>                 suspend_vq(ndev, mvq);
> -       } else {
> +       } else if (mvdev->status & VIRTIO_CONFIG_S_DRIVER_OK) {
>                 if (resume_vq(ndev, mvq))
>                         ready = false;
>         }
> @@ -3078,10 +3078,18 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>                                 goto err_setup;
>                         }
>                         register_link_notifier(ndev);
> -                       err = setup_vq_resources(ndev, true);
> -                       if (err) {
> -                               mlx5_vdpa_warn(mvdev, "failed to setup driver\n");
> -                               goto err_driver;
> +                       if (ndev->setup) {
> +                               err = resume_vqs(ndev);
> +                               if (err) {
> +                                       mlx5_vdpa_warn(mvdev, "failed to resume VQs\n");
> +                                       goto err_driver;
> +                               }
> +                       } else {
> +                               err = setup_vq_resources(ndev, true);
> +                               if (err) {
> +                                       mlx5_vdpa_warn(mvdev, "failed to setup driver\n");
> +                                       goto err_driver;
> +                               }
>                         }
>                 } else {
>                         mlx5_vdpa_warn(mvdev, "did not expect DRIVER_OK to be cleared\n");
> @@ -3142,6 +3150,7 @@ 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);
>         up_write(&ndev->reslock);
>
>         return 0;
> @@ -3836,8 +3845,21 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>                 goto err_reg;
>
>         mgtdev->ndev = ndev;
> +
> +       /* For virtio-vdpa, the device was set up during device register. */
> +       if (ndev->setup)
> +               return 0;
> +
> +       down_write(&ndev->reslock);
> +       err = setup_vq_resources(ndev, false);
> +       up_write(&ndev->reslock);
> +       if (err)
> +               goto err_setup_vq_res;
> +
>         return 0;
>
> +err_setup_vq_res:
> +       _vdpa_unregister_device(&mvdev->vdev);
>  err_reg:
>         destroy_workqueue(mvdev->wq);
>  err_res2:
> @@ -3863,6 +3885,11 @@ static void mlx5_vdpa_dev_del(struct vdpa_mgmt_dev *v_mdev, struct vdpa_device *
>
>         unregister_link_notifier(ndev);
>         _vdpa_unregister_device(dev);
> +
> +       down_write(&ndev->reslock);
> +       teardown_vq_resources(ndev);
> +       up_write(&ndev->reslock);
> +
>         wq = mvdev->wq;
>         mvdev->wq = NULL;
>         destroy_workqueue(wq);
>
> --
> 2.45.1
>