Re: [PATCH v2] vdpa/mlx5: Support interrupt bypassing

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Apr 19, 2023 at 12:39:11PM +0800, Jason Wang wrote:
> On Mon, Apr 17, 2023 at 4:35 PM Eli Cohen <elic@nvidia.com> wrote:
> >
> > Add support for generation of interrupts from the device directly to the
> > VM to the VCPU thus avoiding the overhead on the host CPU.
> >
> > When supported, the driver will attempt to allocate vectors for each
> > data virtqueue. If a vector for a virtqueue cannot be provided it will
> > use the QP mode where notifications go through the driver.
> >
> > In addition, we add a shutdown callback to make sure allocated
> > interrupts are released in case of shutdown to allow clean shutdown.
> >
> > Issue: 2211199
> > Change-Id: I7633ee56ca2861a8d0f4935bb29109c8e80f352c
> > Signed-off-by: Eli Cohen <elic@nvidia.com>
> > Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
> > ---
> > v1 -> v2:
> > 1. Remove parentheses around return statement
> > 2. Immediately return if vector entry found
> > 3. Use boolean instead of counter on used entry tracking
> > 4. Fix symmetry in teardown_vq()
> >
> > This patch is still under discussion but I wanted to address commnents
> > and have this is the basis for further discussion.
> >
> >  drivers/vdpa/mlx5/net/mlx5_vnet.c | 140 ++++++++++++++++++++++++++++--
> >  drivers/vdpa/mlx5/net/mlx5_vnet.h |  14 +++
> >  2 files changed, 145 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > index e29e32b306ad..2360c643148f 100644
> > --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> > @@ -83,6 +83,7 @@ struct mlx5_vq_restore_info {
> >         u64 driver_addr;
> >         u16 avail_index;
> >         u16 used_index;
> > +       struct msi_map map;
> >         bool ready;
> >         bool restore;
> >  };
> > @@ -118,6 +119,7 @@ struct mlx5_vdpa_virtqueue {
> >         u16 avail_idx;
> >         u16 used_idx;
> >         int fw_state;
> > +       struct msi_map map;
> >
> >         /* keep last in the struct */
> >         struct mlx5_vq_restore_info ri;
> > @@ -808,6 +810,13 @@ static bool counters_supported(const struct mlx5_vdpa_dev *mvdev)
> >                BIT_ULL(MLX5_OBJ_TYPE_VIRTIO_Q_COUNTERS);
> >  }
> >
> > +static bool msix_mode_supported(struct mlx5_vdpa_dev *mvdev)
> > +{
> > +       return MLX5_CAP_DEV_VDPA_EMULATION(mvdev->mdev, event_mode) &
> > +               (1 << MLX5_VIRTIO_Q_EVENT_MODE_MSIX_MODE) &&
> > +               pci_msix_can_alloc_dyn(mvdev->mdev->pdev);
> > +}
> > +
> >  static int create_virtqueue(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
> >  {
> >         int inlen = MLX5_ST_SZ_BYTES(create_virtio_net_q_in);
> > @@ -849,9 +858,15 @@ static int create_virtqueue(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtque
> >         if (vq_is_tx(mvq->index))
> >                 MLX5_SET(virtio_net_q_object, obj_context, tisn_or_qpn, ndev->res.tisn);
> >
> > -       MLX5_SET(virtio_q, vq_ctx, event_mode, MLX5_VIRTIO_Q_EVENT_MODE_QP_MODE);
> > +       if (mvq->map.virq) {
> > +               MLX5_SET(virtio_q, vq_ctx, event_mode, MLX5_VIRTIO_Q_EVENT_MODE_MSIX_MODE);
> > +               MLX5_SET(virtio_q, vq_ctx, event_qpn_or_msix, mvq->map.index);
> > +       } else {
> > +               MLX5_SET(virtio_q, vq_ctx, event_mode, MLX5_VIRTIO_Q_EVENT_MODE_QP_MODE);
> > +               MLX5_SET(virtio_q, vq_ctx, event_qpn_or_msix, mvq->fwqp.mqp.qpn);
> > +       }
> > +
> >         MLX5_SET(virtio_q, vq_ctx, queue_index, mvq->index);
> > -       MLX5_SET(virtio_q, vq_ctx, event_qpn_or_msix, mvq->fwqp.mqp.qpn);
> >         MLX5_SET(virtio_q, vq_ctx, queue_size, mvq->num_ent);
> >         MLX5_SET(virtio_q, vq_ctx, virtio_version_1_0,
> >                  !!(ndev->mvdev.actual_features & BIT_ULL(VIRTIO_F_VERSION_1)));
> > @@ -1194,6 +1209,34 @@ static void counter_set_dealloc(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_vir
> >                 mlx5_vdpa_warn(&ndev->mvdev, "dealloc counter set 0x%x\n", mvq->counter_set_id);
> >  }
> >
> > +static void alloc_vector(struct mlx5_vdpa_net *ndev,
> > +                        struct mlx5_vdpa_virtqueue *mvq)
> > +{
> > +       struct mlx5_vdpa_irq_pool *irqp = &ndev->irqp;
> > +       int i;
> > +
> > +       for (i = 0; i < irqp->num_ent; i++) {
> > +               if (!irqp->entries[i].used) {
> > +                       irqp->entries[i].used = true;
> > +                       mvq->map = irqp->entries[i].map;
> > +                       return;
> > +               }
> > +       }
> > +}
> > +
> > +static void dealloc_vector(struct mlx5_vdpa_net *ndev,
> > +                          struct mlx5_vdpa_virtqueue *mvq)
> > +{
> > +       struct mlx5_vdpa_irq_pool *irqp = &ndev->irqp;
> > +       int i;
> > +
> > +       for (i = 0; i < irqp->num_ent; i++)
> > +               if (mvq->map.virq == irqp->entries[i].map.virq) {
> > +                       irqp->entries[i].used = false;
> > +                       return;
> > +               }
> > +}
> > +
> >  static int setup_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
> >  {
> >         u16 idx = mvq->index;
> > @@ -1223,27 +1266,31 @@ static int setup_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *mvq)
> >
> >         err = counter_set_alloc(ndev, mvq);
> >         if (err)
> > -               goto err_counter;
> > +               goto err_connect;
> >
> > +       alloc_vector(ndev, mvq);
> >         err = create_virtqueue(ndev, mvq);
> >         if (err)
> > -               goto err_connect;
> > +               goto err_vq;
> >
> >         if (mvq->ready) {
> >                 err = modify_virtqueue(ndev, mvq, MLX5_VIRTIO_NET_Q_OBJECT_STATE_RDY);
> >                 if (err) {
> >                         mlx5_vdpa_warn(&ndev->mvdev, "failed to modify to ready vq idx %d(%d)\n",
> >                                        idx, err);
> > -                       goto err_connect;
> > +                       goto err_modify;
> >                 }
> >         }
> >
> >         mvq->initialized = true;
> >         return 0;
> >
> > -err_connect:
> > +err_modify:
> > +       destroy_virtqueue(ndev, mvq);
> > +err_vq:
> > +       dealloc_vector(ndev, mvq);
> >         counter_set_dealloc(ndev, mvq);
> > -err_counter:
> > +err_connect:
> >         qp_destroy(ndev, &mvq->vqqp);
> >  err_vqqp:
> >         qp_destroy(ndev, &mvq->fwqp);
> > @@ -1288,6 +1335,7 @@ static void teardown_vq(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqueue *
> >
> >         suspend_vq(ndev, mvq);
> >         destroy_virtqueue(ndev, mvq);
> > +       dealloc_vector(ndev, mvq);
> >         counter_set_dealloc(ndev, mvq);
> >         qp_destroy(ndev, &mvq->vqqp);
> >         qp_destroy(ndev, &mvq->fwqp);
> > @@ -2505,6 +2553,7 @@ static int save_channel_info(struct mlx5_vdpa_net *ndev, struct mlx5_vdpa_virtqu
> >         ri->desc_addr = mvq->desc_addr;
> >         ri->device_addr = mvq->device_addr;
> >         ri->driver_addr = mvq->driver_addr;
> > +       ri->map = mvq->map;
> >         ri->restore = true;
> >         return 0;
> >  }
> > @@ -2549,6 +2598,7 @@ static void restore_channels_info(struct mlx5_vdpa_net *ndev)
> >                 mvq->desc_addr = ri->desc_addr;
> >                 mvq->device_addr = ri->device_addr;
> >                 mvq->driver_addr = ri->driver_addr;
> > +               mvq->map = ri->map;
> >         }
> >  }
> >
> > @@ -2833,6 +2883,21 @@ static struct device *mlx5_get_vq_dma_dev(struct vdpa_device *vdev, u16 idx)
> >         return mvdev->vdev.dma_dev;
> >  }
> >
> > +static void free_irqs(struct mlx5_vdpa_net *ndev)
> > +{
> > +       struct mlx5_vdpa_irq_pool_entry *ent;
> > +       int i;
> > +
> > +       if (!msix_mode_supported(&ndev->mvdev))
> > +               return;
> > +
> > +       for (i = ndev->irqp.num_ent - 1; i >= 0; i--) {
> > +               ent = ndev->irqp.entries + i;
> > +               mlx5_msix_free(ndev->mvdev.mdev, ent->map);
> > +       }
> > +       kfree(ndev->irqp.entries);
> > +}
> > +
> >  static void mlx5_vdpa_free(struct vdpa_device *vdev)
> >  {
> >         struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> > @@ -2848,6 +2913,7 @@ static void mlx5_vdpa_free(struct vdpa_device *vdev)
> >                 mlx5_mpfs_del_mac(pfmdev, ndev->config.mac);
> >         }
> >         mlx5_vdpa_free_resources(&ndev->mvdev);
> > +       free_irqs(ndev);
> >         kfree(ndev->event_cbs);
> >         kfree(ndev->vqs);
> >  }
> > @@ -2876,9 +2942,23 @@ static struct vdpa_notification_area mlx5_get_vq_notification(struct vdpa_device
> >         return ret;
> >  }
> >
> > -static int mlx5_get_vq_irq(struct vdpa_device *vdv, u16 idx)
> > +static int mlx5_get_vq_irq(struct vdpa_device *vdev, u16 idx)
> >  {
> > -       return -EOPNOTSUPP;
> > +       struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
> > +       struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
> > +       struct mlx5_vdpa_virtqueue *mvq;
> > +
> > +       if (!is_index_valid(mvdev, idx))
> > +               return -EINVAL;
> > +
> > +       if (is_ctrl_vq_idx(mvdev, idx))
> > +               return -EOPNOTSUPP;
> > +
> > +       mvq = &ndev->vqs[idx];
> > +       if (!mvq->map.virq)
> > +               return -EOPNOTSUPP;
> > +
> > +       return mvq->map.virq;
> >  }
> >
> >  static u64 mlx5_vdpa_get_driver_features(struct vdpa_device *vdev)
> > @@ -3155,6 +3235,35 @@ static int config_func_mtu(struct mlx5_core_dev *mdev, u16 mtu)
> >         return err;
> >  }
> >
> > +static irqreturn_t int_handler(int irq, void *nh)
> > +{
> > +       return IRQ_HANDLED;
> > +}
> 
> I still don't understand when this handler will be called.
> 
> E.g IFCVF did:
> 
> static irqreturn_t ifcvf_vq_intr_handler(int irq, void *arg)
> {
>         struct vring_info *vring = arg;
> 
>         if (vring->cb.callback)
>                 return vring->cb.callback(vring->cb.private);
> 
>         return IRQ_HANDLED;
> }
> 
> So when the irq bypass doesn't work it will fall back to a slow path.
> 
> Maybe some comments here or changelog would be helpful.
> 
> Thanks

Jason I don't understand what you are asking about.
Are you asking why it's ok not to invoke the vring callback?

-- 
MST

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