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Subject: Re: [PATCH v2 8/8] vsock/virtio: make the RX buffer size tunable
To:     Stefano Garzarella <sgarzare@redhat.com>, netdev@vger.kernel.org
Cc:     "David S. Miller" <davem@davemloft.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        Stefan Hajnoczi <stefanha@redhat.com>
References: <20190510125843.95587-1-sgarzare@redhat.com>
 <20190510125843.95587-9-sgarzare@redhat.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <eddb5a89-ed44-3a65-0181-84f7f27dd2cb@redhat.com>
Date:   Mon, 13 May 2019 18:05:02 +0800
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On 2019/5/10 下午8:58, Stefano Garzarella wrote:
> The RX buffer size determines the memory consumption of the
> vsock/virtio guest driver, so we make it tunable through
> a module parameter.
>
> The size allowed are between 4 KB and 64 KB in order to be
> compatible with old host drivers.
>
> Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>


I don't see much value of doing this through kernel command line. We 
should deal with them automatically like what virtio-net did. Or even a 
module parameter is better.

Thanks


> ---
>   include/linux/virtio_vsock.h     |  1 +
>   net/vmw_vsock/virtio_transport.c | 27 ++++++++++++++++++++++++++-
>   2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 5a9d25be72df..b9f8c3d91f80 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -13,6 +13,7 @@
>   #define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 64)
>   #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
>   #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
> +#define VIRTIO_VSOCK_MIN_PKT_BUF_SIZE		(1024 * 4)
>   
>   enum {
>   	VSOCK_VQ_RX     = 0, /* for host to guest data */
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index af1d2ce12f54..732398b4e28f 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -66,6 +66,31 @@ struct virtio_vsock {
>   	u32 guest_cid;
>   };
>   
> +static unsigned int rx_buf_size = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +
> +static int param_set_rx_buf_size(const char *val, const struct kernel_param *kp)
> +{
> +	unsigned int size;
> +	int ret;
> +
> +	ret = kstrtouint(val, 0, &size);
> +	if (ret)
> +		return ret;
> +
> +	if (size < VIRTIO_VSOCK_MIN_PKT_BUF_SIZE ||
> +	    size > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
> +		return -EINVAL;
> +
> +	return param_set_uint(val, kp);
> +};
> +
> +static const struct kernel_param_ops param_ops_rx_buf_size = {
> +	.set = param_set_rx_buf_size,
> +	.get = param_get_uint,
> +};
> +
> +module_param_cb(rx_buf_size, &param_ops_rx_buf_size, &rx_buf_size, 0644);
> +
>   static struct virtio_vsock *virtio_vsock_get(void)
>   {
>   	return the_virtio_vsock;
> @@ -261,7 +286,7 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
>   
>   static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
>   {
> -	int buf_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> +	int buf_len = rx_buf_size;
>   	struct virtio_vsock_pkt *pkt;
>   	struct scatterlist hdr, buf, *sgs[2];
>   	struct virtqueue *vq;