Re: [RFC PATCH v1] virtio/vsock: allocate multiple skbuffs on tx

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Fri, Mar 17, 2023 at 01:38:39PM +0300, Arseniy Krasnov wrote:
> This adds small optimization for tx path: instead of allocating single
> skbuff on every call to transport, allocate multiple skbuffs until
> credit space allows, thus trying to send as much as possible data without
> return to af_vsock.c.

Hey Arseniy, I really like this optimization. I have a few
questions/comments below.

> 
> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
> ---
>  net/vmw_vsock/virtio_transport_common.c | 45 +++++++++++++++++--------
>  1 file changed, 31 insertions(+), 14 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index 6564192e7f20..cda587196475 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>  	const struct virtio_transport *t_ops;
>  	struct virtio_vsock_sock *vvs;
>  	u32 pkt_len = info->pkt_len;
> -	struct sk_buff *skb;
> +	u32 rest_len;
> +	int ret;
>  
>  	info->type = virtio_transport_get_type(sk_vsock(vsk));
>  
> @@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>  
>  	vvs = vsk->trans;
>  
> -	/* we can send less than pkt_len bytes */
> -	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> -		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
> -
>  	/* virtio_transport_get_credit might return less than pkt_len credit */
>  	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
>  
> @@ -227,17 +224,37 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>  	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
>  		return pkt_len;
>  
> -	skb = virtio_transport_alloc_skb(info, pkt_len,
> -					 src_cid, src_port,
> -					 dst_cid, dst_port);
> -	if (!skb) {
> -		virtio_transport_put_credit(vvs, pkt_len);
> -		return -ENOMEM;
> -	}
> +	rest_len = pkt_len;
>  
> -	virtio_transport_inc_tx_pkt(vvs, skb);
> +	do {
> +		struct sk_buff *skb;
> +		size_t skb_len;
> +
> +		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
> +
> +		skb = virtio_transport_alloc_skb(info, skb_len,
> +						 src_cid, src_port,
> +						 dst_cid, dst_port);
> +		if (!skb) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}

In this case, if a previous round of the loop succeeded with send_pkt(),
I think that we may still want to return the number of bytes that have
successfully been sent so far?

>  
> -	return t_ops->send_pkt(skb);
> +		virtio_transport_inc_tx_pkt(vvs, skb);
> +
> +		ret = t_ops->send_pkt(skb);
> +
> +		if (ret < 0)
> +			goto out;

Ditto here.

> +
> +		rest_len -= skb_len;
> +	} while (rest_len);
> +
> +	return pkt_len;
> +
> +out:
> +	virtio_transport_put_credit(vvs, rest_len);
> +	return ret;
>  }
>  
>  static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> -- 
> 2.25.1