Re: [dpdk-dev] [PATCH v2 1/7] mbuf: new function to generate raw Tx offload value

[Shahaf Shuler <shahafs@mellanox.com>]

Hi Konstantin,

Wednesday, March 20, 2019 8:47 PM, Konstantin Ananyev:
> Subject: [dpdk-dev] [PATCH v2 1/7] mbuf: new function to generate raw Tx
> offload value
> 
> Operations to set/update bit-fields often cause compilers to generate
> suboptimal code.
> To help avoid such situation for tx_offload fields:
> introduce new enum for tx_offload bit-fields lengths and offsets, and new
> function to generate raw tx_offload value.
> 
> Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> ---
>  lib/librte_mbuf/rte_mbuf.h | 71
> ++++++++++++++++++++++++++++++++++----
>  1 file changed, 64 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index
> d961ccaf6..b967ad17e 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -479,6 +479,26 @@ struct rte_mbuf_sched {
>  	uint16_t reserved;   /**< Reserved. */
>  }; /**< Hierarchical scheduler */
> 
> +/** enum for the tx_offload bit-fields lenghts and offsets. */ enum {
> +	RTE_MBUF_L2_LEN_BITS = 7,
> +	RTE_MBUF_L3_LEN_BITS = 9,
> +	RTE_MBUF_L4_LEN_BITS = 8,
> +	RTE_MBUF_TSO_SEGSZ_BITS = 16,
> +	RTE_MBUF_OL3_LEN_BITS = 9,
> +	RTE_MBUF_OL2_LEN_BITS = 7,
> +	RTE_MBUF_L2_LEN_OFS = 0,
> +	RTE_MBUF_L3_LEN_OFS = RTE_MBUF_L2_LEN_OFS +
> RTE_MBUF_L2_LEN_BITS,
> +	RTE_MBUF_L4_LEN_OFS = RTE_MBUF_L3_LEN_OFS +
> RTE_MBUF_L3_LEN_BITS,
> +	RTE_MBUF_TSO_SEGSZ_OFS = RTE_MBUF_L4_LEN_OFS +
> RTE_MBUF_L4_LEN_BITS,
> +	RTE_MBUF_OL3_LEN_OFS = RTE_MBUF_TSO_SEGSZ_OFS +
> RTE_MBUF_TSO_SEGSZ_BITS,
> +	RTE_MBUF_OL2_LEN_OFS = RTE_MBUF_OL3_LEN_OFS +
> RTE_MBUF_OL3_LEN_BITS,
> +	RTE_MBUF_TXOFLD_UNUSED_OFS =
> +		RTE_MBUF_OL2_LEN_OFS + RTE_MBUF_OL2_LEN_BITS,
> +	RTE_MBUF_TXOFLD_UNUSED_BITS =
> +		sizeof(uint64_t) * CHAR_BIT -
> RTE_MBUF_TXOFLD_UNUSED_OFS, };
> +
>  /**
>   * The generic rte_mbuf, containing a packet mbuf.
>   */
> @@ -640,19 +660,24 @@ struct rte_mbuf {
>  		uint64_t tx_offload;       /**< combined for easy fetch */
>  		__extension__
>  		struct {
> -			uint64_t l2_len:7;
> +			uint64_t l2_len:RTE_MBUF_L2_LEN_BITS;
>  			/**< L2 (MAC) Header Length for non-tunneling pkt.
>  			 * Outer_L4_len + ... + Inner_L2_len for tunneling
> pkt.
>  			 */
> -			uint64_t l3_len:9; /**< L3 (IP) Header Length. */
> -			uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length.
> */
> -			uint64_t tso_segsz:16; /**< TCP TSO segment size */
> +			uint64_t l3_len:RTE_MBUF_L3_LEN_BITS;
> +			/**< L3 (IP) Header Length. */
> +			uint64_t l4_len:RTE_MBUF_L4_LEN_BITS;
> +			/**< L4 (TCP/UDP) Header Length. */
> +			uint64_t tso_segsz:RTE_MBUF_TSO_SEGSZ_BITS;
> +			/**< TCP TSO segment size */
> 
>  			/* fields for TX offloading of tunnels */
> -			uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr
> Length. */
> -			uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr
> Length. */
> +			uint64_t outer_l3_len:RTE_MBUF_OL3_LEN_BITS;
> +			/**< Outer L3 (IP) Hdr Length. */
> +			uint64_t outer_l2_len:RTE_MBUF_OL2_LEN_BITS;
> +			/**< Outer L2 (MAC) Hdr Length. */
> 
> -			/* uint64_t unused:8; */
> +			/* uint64_t
> unused:RTE_MBUF_TXOFLD_UNUSED_BITS; */

I am not sure we want to decide now that this remaining byte is for another Tx offloads.
Maybe it is better to change a bit the rte_mbuf_tx_offload API to receive also the mbuf and to assign the offload values w/ mask. 

>  		};
>  	};
> 
> @@ -2243,6 +2268,38 @@ static inline int rte_pktmbuf_chain(struct
> rte_mbuf *head, struct rte_mbuf *tail
>  	return 0;
>  }
> 
> +/*
> + * @warning
> + * @b EXPERIMENTAL: This API may change without prior notice.
> + *
> + * For given input values generate raw tx_offload value.
> + * @param il2
> + *   l2_len value.
> + * @param il3
> + *   l3_len value.
> + * @param il4
> + *   l4_len value.
> + * @param tso
> + *   tso_segsz value.
> + * @param ol3
> + *   outer_l3_len value.
> + * @param ol2
> + *   outer_l2_len value.
> + * @return
> + *   raw tx_offload value.
> + */
> +static inline uint64_t
> +rte_mbuf_tx_offload(uint64_t il2, uint64_t il3, uint64_t il4, uint64_t tso,
> +	uint64_t ol3, uint64_t ol2)
> +{
> +	return il2 << RTE_MBUF_L2_LEN_OFS |
> +		il3 << RTE_MBUF_L3_LEN_OFS |
> +		il4 << RTE_MBUF_L4_LEN_OFS |
> +		tso << RTE_MBUF_TSO_SEGSZ_OFS |
> +		ol3 << RTE_MBUF_OL3_LEN_OFS |
> +		ol2 << RTE_MBUF_OL2_LEN_OFS;
> +}
> +
>  /**
>   * Validate general requirements for Tx offload in mbuf.
>   *
> --
> 2.17.1