linux-kernel - Re: [PATCH v2 1/3] virtio-net: Introduce extended RSC feature

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Date:   Sun, 1 Mar 2020 06:31:11 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Yuri Benditovich <yuri.benditovich@...nix.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, yan@...nix.com
Subject: Re: [PATCH v2 1/3] virtio-net: Introduce extended RSC feature

On Sun, Mar 01, 2020 at 01:07:31PM +0200, 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>
> ---
>  include/uapi/linux/virtio_net.h | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index a3715a3224c1..536152fad3c4 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -57,6 +57,7 @@
>  					 * Steering */
>  #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
>  
> +#define VIRTIO_NET_F_RSC_EXT	  61	/* extended coalescing info */
>  #define VIRTIO_NET_F_STANDBY	  62	/* Act as standby for another device
>  					 * with the same MAC.
>  					 */
> @@ -104,6 +105,7 @@ 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 info 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) */
> @@ -113,8 +115,14 @@ struct virtio_net_hdr_v1 {
>  	__u8 gso_type;
>  	__virtio16 hdr_len;	/* Ethernet + IP + tcp/udp hdrs */
>  	__virtio16 gso_size;	/* Bytes to append to hdr_len per frame */
> -	__virtio16 csum_start;	/* Position to start checksumming from */
> -	__virtio16 csum_offset;	/* Offset after that to place checksum */
> +	union {
> +		__virtio16 csum_start;	/* Position to start checksumming from */
> +		__le16 rsc_ext_num_packets; /* num of coalesced packets */
> +	};
> +	union {
> +		__virtio16 csum_offset;	/* Offset after that to place checksum */
> +		__le16 rsc_ext_num_dupacks; /* num of duplicated acks */

dupacks -> dup_acks ?

Also wouldn't it be cleaner to have an rsc struct? And "num" is kind of
extraneous, right?
So how about we group the fields:

union {
	/* Unnamed struct for compatiblity. */
	struct {
		csum_start
		csum_offset
	};
	struct {
		virtio16 start;
		virtio16 offset;
	} csum;
	struct {
		le16 packets;
		le16 dup_acks;
	} rsc;
};


what do you think?


> +	};
>  	__virtio16 num_buffers;	/* Number of merged rx buffers */
>  };



> -- 
> 2.17.1