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

[Dragos Tatulea <dtatulea@nvidia.com>]

On Wed, 2024-06-19 at 17:54 +0200, Eugenio Perez Martin wrote:
> On Mon, Jun 17, 2024 at 5:09 PM Dragos Tatulea <dtatulea@nvidia.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?
> 
I don't understand your question, could you rephrase or provide more context
please?

Thanks,
Dragos

> > 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);
> > 
> > --
> > 2.45.1
> > 
>