On Thu, Apr 11, 2024 at 09:09:49AM GMT, Paolo Abeni wrote:

On Mon, 2024-04-08 at 15:37 +0200, Luigi Leonardi wrote:

quoted

This patch introduce support for stream_bytes_unsent and
seqpacket_bytes_unsent ioctl for virtio_transport, vhost_vsock
and vsock_loopback.

For all transports the unsent bytes counter is incremented
in virtio_transport_send_pkt_info.

In the virtio_transport (G2H) the counter is decremented each time the host
notifies the guest that it consumed the skbuffs.
In vhost-vsock (H2G) the counter is decremented after the skbuff is queued
in the virtqueue.
In vsock_loopback the counter is decremented after the skbuff is
dequeued.

Signed-off-by: Luigi Leonardi <redacted>

I think this deserve an explicit ack from Stefano, and Stefano can't
review patches in the next few weeks. If it's not urgent this will have
to wait a bit.

quoted

---
 drivers/vhost/vsock.c                   |  4 ++-
 include/linux/virtio_vsock.h            |  7 ++++++
 net/vmw_vsock/virtio_transport.c        |  4 ++-
 net/vmw_vsock/virtio_transport_common.c | 33 +++++++++++++++++++++++++
 net/vmw_vsock/vsock_loopback.c          |  7 ++++++
 5 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index ec20ecff85c7..dba8b3ea37bf 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -244,7 +244,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 					restart_tx = true;
 			}

-			consume_skb(skb);
+			virtio_transport_consume_skb_sent(skb, true);
 		}
 	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
 	if (added)

@@ -451,6 +451,8 @@ static struct virtio_transport vhost_transport = {
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,

+		.unsent_bytes             = virtio_transport_bytes_unsent,
+
 		.read_skb = virtio_transport_read_skb,
 	},

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index c82089dee0c8..dbb22d45d203 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h

@@ -134,6 +134,8 @@ struct virtio_vsock_sock {
 	u32 peer_fwd_cnt;
 	u32 peer_buf_alloc;

+	atomic_t bytes_unsent;

This will add 2 atomic operations per packet, possibly on contended
cachelines. Have you considered leveraging the existing transport-level
lock to protect the counter updates?

Good point!

Maybe we can handle it together with `tx_cnt` in
virtio_transport_get_credit()/virtio_transport_put_credit().

Eventually these are called exactly to count the payload we are sending
(`tx_cnt` is a counter that only grows, virtio_transport_put_credit() is
called only to return unused credit, so we can't use it directly but
always need a new variable like `bytes_unsent`).

I mean something like this (untested at all):

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index dbb22d45d203..713197c16b7f 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h

@@ -133,8 +133,7 @@ struct virtio_vsock_sock {
         u32 tx_cnt;
         u32 peer_fwd_cnt;
         u32 peer_buf_alloc;
-
-       atomic_t bytes_unsent;
+       u32 bytes_unsent;

         /* Protected by rx_lock */
         u32 fwd_cnt;

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 82a31a13dc32..b1a51db616cf 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -419,13 +419,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
                  */
                 rest_len -= ret;

-               /* Avoid to perform an atomic_add on 0 bytes.
-                * This is equivalent to check on VIRTIO_VSOCK_OP_RW
-                * as is the only packet type with payload.
-                */
-               if (ret)
-                       atomic_add(ret, &vvs->bytes_unsent);
-
                 if (WARN_ONCE(ret != skb_len,
                               "'send_pkt()' returns %i, but %zu expected\n",
                               ret, skb_len))

@@ -479,7 +472,10 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
                 struct virtio_vsock_sock *vvs;

                 vvs = vs->trans;
-               atomic_sub(skb->len, &vvs->bytes_unsent);
+
+               spin_lock_bh(&vvs->tx_lock);
+               vvs->bytes_unsent -= skb->len;
+               spin_unlock_bh(&vvs->tx_lock);
         }

         if (consume)

@@ -499,6 +495,7 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
         if (ret > credit)
                 ret = credit;
         vvs->tx_cnt += ret;
+       vvs->bytes_unsent += ret;
         spin_unlock_bh(&vvs->tx_lock);

         return ret;

@@ -512,6 +509,7 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit)

         spin_lock_bh(&vvs->tx_lock);
         vvs->tx_cnt -= credit;
+       vvs->bytes_unsent -= ret;
         spin_unlock_bh(&vvs->tx_lock);
  }
  EXPORT_SYMBOL_GPL(virtio_transport_put_credit);

@@ -915,7 +913,6 @@ int virtio_transport_do_socket_init(struct vsock_sock *vsk,
                 vsk->buffer_size = VIRTIO_VSOCK_MAX_BUF_SIZE;

         vvs->buf_alloc = vsk->buffer_size;
-       atomic_set(&vvs->bytes_unsent, 0);

         spin_lock_init(&vvs->rx_lock);
         spin_lock_init(&vvs->tx_lock);

@@ -1118,8 +1115,13 @@ EXPORT_SYMBOL_GPL(virtio_transport_destruct);
  int virtio_transport_bytes_unsent(struct vsock_sock *vsk)
  {
         struct virtio_vsock_sock *vvs = vsk->trans;
+       int ret;

-       return atomic_read(&vvs->bytes_unsent);
+       spin_lock_bh(&vvs->tx_lock);
+       ret = vvs->bytes_unsent;
+       spin_unlock_bh(&vvs->tx_lock);
+
+       return ret;
  }
  EXPORT_SYMBOL_GPL(virtio_transport_bytes_unsent);

WDYT?

Should virtio_transport_bytes_unsent() returns size_t?

Thanks,
Stefano