netdev - Re: [RFC v2 3/7] vsock: batch buffers in tx

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Date:   Thu, 25 Aug 2022 15:08:58 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Guo Zhi <qtxuning1999@...u.edu.cn>, eperezma@...hat.com,
        sgarzare@...hat.com, mst@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [RFC v2 3/7] vsock: batch buffers in tx


在 2022/8/17 21:57, Guo Zhi 写道:
> 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 <qtxuning1999@...u.edu.cn>
> ---
>   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


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