Re: [dpdk-dev] [PATCH v7 14/15] vhost: add notification for packed ring

[Maxime Coquelin]

On 07/05/2018 07:12 AM, Tiwei Bie wrote:

On Wed, Jul 04, 2018 at 11:54:37PM +0200, Maxime Coquelin wrote:
[...]

@@ -225,6 +231,15 @@ struct vring_desc_packed {
        uint16_t index;
        uint16_t flags;
  };
+
+#define VRING_EVENT_F_ENABLE 0x0
+#define VRING_EVENT_F_DISABLE 0x1
+#define VRING_EVENT_F_DESC 0x2
+
+struct vring_packed_desc_event {
+       uint16_t desc_event_off_wrap;
+       uint16_t desc_event_flags;
+};

As all above types (including struct vring_desc_packed)
and macros are being protected by VIRTIO_F_RING_PACKED,
and they won't be defined if VIRTIO_F_RING_PACKED is
defined in kernel header. We may want to unify the names.

For the types, we may have below types defined in
linux uapi:

struct vring_packed;
struct vring_packed_desc;
struct vring_packed_desc_event;

They can also be named as:

struct vring_packed;
struct vring_desc_packed;
struct vring_packed_desc_event;

We need to choose one of them or something else.

For the `struct vring_packed_desc_event`, it can
be defined as:

struct vring_packed_desc_event {
        uint16_t off_wrap;
        uint16_t flags;
};

or

struct vring_packed_desc_event {
        uint16_t desc_event_off_wrap;
        uint16_t desc_event_flags;
};

We need to choose one of them or something else.

For the `struct vring_packed_desc`, it can be
defined as:

struct vring_packed_desc {
        uint64_t addr;
        uint32_t len;
        uint16_t index;
        uint16_t flags;
};

or

struct vring_packed_desc {
        uint64_t addr;
        uint32_t len;
        uint16_t id;            // index -> id
        uint16_t flags;
};

We need to choose one of them or something else.

I will align on Kernel header.

  #endif

[...]

+static __rte_always_inline void
+vhost_vring_call_packed(struct virtio_net *dev, struct vhost_virtqueue *vq)
+{
+       uint16_t old, new, off, off_wrap;
+       bool kick = false;
+
+       /* Flush used desc update. */
+       rte_smp_mb();
+
+       if (!(dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))) {
+               if (vq->driver_event->desc_event_flags !=
+                               VRING_EVENT_F_DISABLE)
+                       kick = true;
+               goto kick;
+       }
+
+       old = vq->signalled_used;

We also need to check whether vq->signalled_used is valid?

Yes, thanks for pointing this out.

So if not valid, I'll kick if desc_event_flags != VRING_EVENT_F_DISABLE.

+       new = vq->last_used_idx;
+       vq->signalled_used = new;
+
+       if (vq->driver_event->desc_event_flags != VRING_EVENT_F_DESC) {
+               if (vq->driver_event->desc_event_flags !=
+                               VRING_EVENT_F_DISABLE)
+                       kick = true;
+               goto kick;
+       }
+
+       rte_smp_rmb();
+
+       off_wrap = vq->driver_event->desc_event_off_wrap;
+       off = off_wrap & ~(1 << 15);
+
+       if (vq->used_wrap_counter != off_wrap >> 15)
+               off -= vq->size;
+
+       if (vhost_need_event(off, new, old))
+               kick = true;

If new <= old, old needs to -= vq->size?

Right, I'll fix it in next version.

Thanks!
Maxime

+kick:
+       if (kick)
+               eventfd_write(vq->callfd, (eventfd_t)1);
+}
+

[...]