Re: [PATCH vhost 20/23] vdpa/mlx5: Pre-create hardware VQs at vdpa .dev_add time

Zhu Yanjun
2024-07-08T16:22:30Z

在 2024/6/17 17:07, Dragos Tatulea 写道:
> 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.

Hi, Dragos Tatulea

From the above, when a device is created, all the VQs and their
associated resources are also created.
If VM live migration does not occur, how much resources are wasted?

I mean, to achieve a better downtime, how much resource are used?

"
On a 64 CPU, 256 GB VM with 1 vDPA device of 16 VQps, the full VQ
resource creation + resume time was ~370ms. Now it's down to 60 ms
(only VQ config and resume). The measurements were done on a ConnectX6DX
based vDPA device.
"
From the above, the performance is amazing.
If we expect to use it in the production hosts, how much resources
should we prepare to achieve this downtime?

Zhu Yanjun

>
> 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.
>
> Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> Reviewed-by: Cosmin Ratiu <cratiu@nvidia.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);
>