Re: [RFC v3 3/7] vsock: batch buffers in tx

----- Original Message -----

From: "jasowang" <redacted>
To: "Guo Zhi" <redacted>, "eperezma" <eperezma@redhat.com>, "sgarzare" <sgarzare@redhat.com>, "Michael
Tsirkin" [off-list ref]
Cc: "netdev" <redacted>, "linux-kernel" <redacted>, "kvm list" <redacted>,
"virtualization" [off-list ref]
Sent: Wednesday, September 7, 2022 12:27:40 PM
Subject: Re: [RFC v3 3/7] vsock: batch buffers in tx

在 2022/9/1 13:54, Guo Zhi 写道:

quoted

Vsock uses buffers in order, and for tx driver doesn't have to
know the length of the buffer. So we can do a batch for vsock if
in order negotiated, only write one used ring for a batch of buffers

Signed-off-by: Guo Zhi <redacted>
---
  drivers/vhost/vsock.c | 12 ++++++++++--
  1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 368330417bde..e08fbbb5439e 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -497,7 +497,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work

*work)
  	struct vhost_vsock *vsock = container_of(vq->dev, struct vhost_vsock,
  						 dev);
  	struct virtio_vsock_pkt *pkt;
-	int head, pkts = 0, total_len = 0;
+	int head, pkts = 0, total_len = 0, add = 0;
  	unsigned int out, in;
  	bool added = false;
  

@@ -551,10 +551,18 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work

*work)
  		else
  			virtio_transport_free_pkt(pkt);
  
-		vhost_add_used(vq, head, 0);
+		if (!vhost_has_feature(vq, VIRTIO_F_IN_ORDER)) {
+			vhost_add_used(vq, head, 0);

I'd do this step by step.

1) switch to use vhost_add_used_n() for vsock, less copy_to_user()
better performance
2) do in-order on top

LGTM!, I think it is the correct way.

quoted

+		} else {
+			vq->heads[add].id = head;
+			vq->heads[add++].len = 0;

How can we guarantee that we are in the boundary of the heads array?

Btw in the case of in-order we don't need to record the heads, instead
we just need to know the head of the last buffer, it reduces the stress
on the cache.

Thanks

Yeah, I will change this and only copy last head for in order feature.

Thanks

quoted

+		}
  		added = true;
  	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
  
+	/* If in order feature negotiaged, we can do a batch to increase performance
*/
+	if (vhost_has_feature(vq, VIRTIO_F_IN_ORDER) && added)
+		vhost_add_used_n(vq, vq->heads, add);
  no_more_replies:
  	if (added)
  		vhost_signal(&vsock->dev, vq);