Merge branch 'vsock-virtio' into main

Luigi Leonardi says:

====================
vsock: avoid queuing on intermediate queue if possible

This series introduces an optimization for vsock/virtio to reduce latency
and increase the throughput: When the guest sends a packet to the host,
and the intermediate queue (send_pkt_queue) is empty, if there is enough
space, the packet is put directly in the virtqueue.

v3->v4
While running experiments on fio with 64B payload, I realized that there
was a mistake in my fio configuration, so I re-ran all the experiments
and now the latency numbers are indeed lower with the patch applied.
I also noticed that I was kicking the host without the lock.

- Fixed a configuration mistake on fio and re-ran all experiments.
- Fio latency measurement using 64B payload.
- virtio_transport_send_skb_fast_path sends kick with the tx_lock acquired
- Addressed all minor style changes requested by maintainer.
- Rebased on latest net-next
- Link to v3: https://lore.kernel.org/r/20240711-pinna-v3-0-697d4164fe80@outlook.com

v2->v3
- Performed more experiments using iperf3 using multiple streams
- Handling of reply packets removed from virtio_transport_send_skb,
  as is needed just by the worker.
- Removed atomic_inc/atomic_sub when queuing directly to the vq.
- Introduced virtio_transport_send_skb_fast_path that handles the
  steps for sending on the vq.
- Fixed a missing mutex_unlock in error path.
- Changed authorship of the second commit
- Rebased on latest net-next

v1->v2
In this v2 I replaced a mutex_lock with a mutex_trylock because it was
insidea RCU critical section. I also added a check on tx_run, so if the
module is being removed the packet is not queued. I'd like to thank Stefano
for reporting the tx_run issue.

Applied all Stefano's suggestions:
    - Minor code style changes
    - Minor commit text rewrite
Performed more experiments:
     - Check if all the packets go directly to the vq (Matias' suggestion)
     - Used iperf3 to see if there is any improvement in overall throughput
      from guest to host
     - Pinned the vhost process to a pCPU.
     - Run fio using 512B payload
Rebased on latest net-next
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
index 6dea6119f5b2..6e78927a598e 100644
--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -98,6 +98,8 @@ static struct virtio_transport loopback_transport = {
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
 
+		.unsent_bytes             = virtio_transport_unsent_bytes,
+
 		.read_skb = virtio_transport_read_skb,
 	},
 
@@ -123,6 +125,10 @@ static void vsock_loopback_work(struct work_struct *work)
 	spin_unlock_bh(&vsock->pkt_queue.lock);
 
 	while ((skb = __skb_dequeue(&pkts))) {
+		/* Decrement the bytes_unsent counter without deallocating skb
+		 * It is freed by the receiver.
+		 */
+		virtio_transport_consume_skb_sent(skb, false);
 		virtio_transport_deliver_tap_pkt(skb);
 		virtio_transport_recv_pkt(&loopback_transport, skb);
 	}