linux-kernel - Re: [PATCH v2] virtio-net: Introduce extended RSC feature

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Date:   Mon, 13 Jan 2020 19:07:52 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yuri Benditovich <yuri.benditovich@...nix.com>, mst@...hat.com,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     yan@...nix.com
Subject: Re: [PATCH v2] virtio-net: Introduce extended RSC feature


On 2020/1/13 下午4:17, Yuri Benditovich wrote:
> VIRTIO_NET_F_RSC_EXT feature bit indicates that the device
> is able to provide extended RSC information. When the feature
> is negotiatede and 'gso_type' field in received packet is not
> GSO_NONE, the device reports number of coalesced packets in
> 'csum_start' field and number of duplicated acks in 'csum_offset'
> field and sets VIRTIO_NET_HDR_F_RSC_INFO in 'flags' field.
>
> Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>


Hi Yuri:

Is the feature used by Linux? If yes, it's better to include the real user.


> ---
>   include/uapi/linux/virtio_net.h | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index a3715a3224c1..2bdd26f8a4ed 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -56,7 +56,7 @@
>   #define VIRTIO_NET_F_MQ	22	/* Device supports Receive Flow
>   					 * Steering */
>   #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
> -
> +#define VIRTIO_NET_F_RSC_EXT	  61	/* Provides extended RSC info */


Is this better to keep the newline around?


>   #define VIRTIO_NET_F_STANDBY	  62	/* Act as standby for another device
>   					 * with the same MAC.
>   					 */
> @@ -104,6 +104,7 @@ struct virtio_net_config {
>   struct virtio_net_hdr_v1 {
>   #define VIRTIO_NET_HDR_F_NEEDS_CSUM	1	/* Use csum_start, csum_offset */
>   #define VIRTIO_NET_HDR_F_DATA_VALID	2	/* Csum is valid */
> +#define VIRTIO_NET_HDR_F_RSC_INFO	4	/* rsc_ext data in csum_ fields */
>   	__u8 flags;
>   #define VIRTIO_NET_HDR_GSO_NONE		0	/* Not a GSO frame */
>   #define VIRTIO_NET_HDR_GSO_TCPV4	1	/* GSO frame, IPv4 TCP (TSO) */
> @@ -118,6 +119,13 @@ struct virtio_net_hdr_v1 {
>   	__virtio16 num_buffers;	/* Number of merged rx buffers */
>   };
>   
> +/*
> + * if VIRTIO_NET_F_RSC_EXT feature has been negotiated and
> + * VIRTIO_NET_HDR_F_RSC_INFO is set in RX packet
> + */
> +#define virtio_net_rsc_ext_num_packets	csum_start
> +#define virtio_net_rsc_ext_num_dupacks	csum_offset


This looks sub-optimal, it looks to me union is better?

Thanks


> +
>   #ifndef VIRTIO_NET_NO_LEGACY
>   /* This header comes first in the scatter-gather list.
>    * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must