Subject: Re: [PATCH net-next 1/3] net: ethtool: extend ringparam set/get APIs for tx_push

From: Jakub Kicinski <[email-masked]>
Date: Fri, 8 Apr 2022 14:55:44 -0700

On Fri, 8 Apr 2022 15:12:43 +0800 Guangbin Huang wrote:
> From: Jie Wang <[email-masked]>
> 
> Currently tx push is a standard driver feature which controls use of a fast
> path descriptor push. So this patch extends the ringparam APIs and data
> structures to support set/get tx push by ethtool -G/g.
> 
> Signed-off-by: Jie Wang <[email-masked]>
> Signed-off-by: Guangbin Huang <[email-masked]>

> +``ETHTOOL_A_RINGS_TX_PUSH`` flag is used to choose the ordinary path or the fast
> +path to send packets. In ordinary path, driver fills BDs to DDR memory and
> +notifies NIC hardware. In fast path, driver pushes BDs to the device memory
> +directly and thus reducing the sending latencies. Setting tx push attribute "on"
> +will enable tx push mode and send packets in fast path if packet size matches.
> +For those not supported hardwares, this attributes is "off" by default settings.

Since you need to respin to fix the kdoc warning - could you also add 
a mention that enabling this feature may increase CPU cost? Unless it's
not the case for your implementation, I thought it usually is..

>  RINGS_SET
>  =========
> @@ -887,6 +894,7 @@ Request contents:
>    ``ETHTOOL_A_RINGS_TX``                u32     size of TX ring
>    ``ETHTOOL_A_RINGS_RX_BUF_LEN``        u32     size of buffers on the ring
>    ``ETHTOOL_A_RINGS_CQE_SIZE``          u32     Size of TX/RX CQE
> +  ``ETHTOOL_A_RINGS_TX_PUSH``           u8      flag of TX Push mode
>    ====================================  ======  ===========================
>  
>  Kernel checks that requested ring sizes do not exceed limits reported by
> diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
> index 4af58459a1e7..ede4f9154cd2 100644
> --- a/include/linux/ethtool.h
> +++ b/include/linux/ethtool.h
> @@ -71,11 +71,13 @@ enum {
>   * struct kernel_ethtool_ringparam - RX/TX ring configuration
>   * @rx_buf_len: Current length of buffers on the rx ring.
>   * @tcp_data_split: Scatter packet headers and data to separate buffers
> + * @tx_push: The flag of tx push mode
>   * @cqe_size: Size of TX/RX completion queue event
>   */
>  struct kernel_ethtool_ringparam {
>  	u32	rx_buf_len;
>  	u8	tcp_data_split;
> +	u8	tx_push;
>  	u32	cqe_size;
>  };
>  
> @@ -87,6 +89,7 @@ struct kernel_ethtool_ringparam {
>  enum ethtool_supported_ring_param {
>  	ETHTOOL_RING_USE_RX_BUF_LEN = BIT(0),
>  	ETHTOOL_RING_USE_CQE_SIZE   = BIT(1),
> +	ETHTOOL_RING_USE_TX_PUSH    = BIT(2),

include/linux/ethtool.h:94: warning: Enum value 'ETHTOOL_RING_USE_TX_PUSH' not described in enum 'ethtool_supported_ring_param'