On Fri, Jun 14, 2024 at 03:55:43PM GMT, Luigi Leonardi wrote:
From: Marco Pinna <marco.pinn95@xxxxxxxxx>
This introduces an optimization in virtio_transport_send_pkt:
when the work queue (send_pkt_queue) is empty the packet is
put directly in the virtqueue reducing latency.
In the following benchmark (pingpong mode) the host sends
a payload to the guest and waits for the same payload back.
Tool: Fio version 3.37-56
Env: Phys host + L1 Guest
Payload: 4k
Runtime-per-test: 50s
Mode: pingpong (h-g-h)
Test runs: 50
Type: SOCK_STREAM
Before (Linux 6.8.11)
------
mean(1st percentile): 722.45 ns
mean(overall): 1686.23 ns
mean(99th percentile): 35379.27 ns
After
------
mean(1st percentile): 602.62 ns
mean(overall): 1248.83 ns
mean(99th percentile): 17557.33 ns
Cool, thanks for this improvement!
Can you also report your host CPU detail?
Co-developed-by: Luigi Leonardi <luigi.leonardi@xxxxxxxxxxx>
Signed-off-by: Luigi Leonardi <luigi.leonardi@xxxxxxxxxxx>
Signed-off-by: Marco Pinna <marco.pinn95@xxxxxxxxx>
---
net/vmw_vsock/virtio_transport.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index c930235ecaec..e89bf87282b2 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -214,7 +214,9 @@ virtio_transport_send_pkt(struct sk_buff *skb)
{
struct virtio_vsock_hdr *hdr;
struct virtio_vsock *vsock;
+ bool use_worker = true;
int len = skb->len;
+ int ret = -1;
Please define ret in the block we use it. Also, we don't need to initialize it.
hdr = virtio_vsock_hdr(skb);
@@ -235,8 +237,34 @@ virtio_transport_send_pkt(struct sk_buff *skb)
if (virtio_vsock_skb_reply(skb))
atomic_inc(&vsock->queued_replies);
- virtio_vsock_skb_queue_tail(&vsock->send_pkt_queue, skb);
- queue_work(virtio_vsock_workqueue, &vsock->send_pkt_work);
+ /* If the send_pkt_queue is empty there is no need to enqueue the packet.
We should clarify which queue. I mean we are always queueing the packet
somewhere, or in the internal queue for the worker or in the virtqueue,
so this comment is not really clear.
+ * Just put it on the ringbuff using virtio_transport_send_skb.
ringbuff? Do you mean virtqueue?
+ */
+
we can avoid this empty line.
+ if (skb_queue_empty_lockless(&vsock->send_pkt_queue)) {
+ bool restart_rx = false;
+ struct virtqueue *vq;
... `int ret;` here.
+
+ mutex_lock(&vsock->tx_lock);
+
+ vq = vsock->vqs[VSOCK_VQ_TX];
+
+ ret = virtio_transport_send_skb(skb, vq, vsock, &restart_rx);
Ah, at the end we don't need `ret` at all.
What about just `if (!virtio_transport_send_skb())`?
+ if (ret == 0) {
+ use_worker = false;
+ virtqueue_kick(vq);
+ }
+
+ mutex_unlock(&vsock->tx_lock);
+
+ if (restart_rx)
+ queue_work(virtio_vsock_workqueue, &vsock->rx_work);
+ }
+
+ if (use_worker) {
+ virtio_vsock_skb_queue_tail(&vsock->send_pkt_queue, skb);
+ queue_work(virtio_vsock_workqueue, &vsock->send_pkt_work);
+ }
out_rcu:
rcu_read_unlock();
--
2.45.2
