Re: [RFC v2 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: Thursday, August 25, 2022 3:08:58 PM
Subject: Re: [RFC v2 3/7] vsock: batch buffers in tx

在 2022/8/17 21:57, 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 | 9 ++++++++-
  1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 368330417bde..b0108009c39a 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c

@@ -500,6 +500,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work

*work)
  	int head, pkts = 0, total_len = 0;
  	unsigned int out, in;
  	bool added = false;
+	int last_head = -1;
  
  	mutex_lock(&vq->mutex);
  

@@ -551,10 +552,16 @@ 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);
+		else
+			last_head = head;
  		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) && last_head != -1)
+		vhost_add_used(vq, last_head, 0);

I may miss something but spec said "The device then skips forward in the
ring according to the size of the batch. ".

I don't see how it is done here.

Thanks

It can skip them in __vhost_add_used_n if _F_IN_ORDER is negotiated.
last_used_idx will be added by size of the batch.

quoted

  no_more_replies:
  	if (added)
  		vhost_signal(&vsock->dev, vq);