Re: [dpdk-dev] [PATCH] mbuf: align rte_mbuf for Windows

[Thomas Monjalon <thomas@monjalon.net>]

+Cc more maintainers

19/05/2020 20:41, talshn@mellanox.com:
> From: Tal Shnaiderman <talshn@mellanox.com>
> 
> Using uint32_t type bit-fields in Windows will pads the
> 'L2/L3/L4 and tunnel information' union with additional bits.
> 
> This padding causes rte_mbuf size misalignment and the total size
> increases to 3 cache-lines.
> 
> Changed packet_type bit-fields types from uint32_t to uint8_t
> to allow unified 2 cache-line structure size.
> 
> Added the __extension__ attribute over the modified struct to avoid
> the warning:
> 
> type of bit-field ... is a GCC extension [-pedantic]
> 
> Signed-off-by: Tal Shnaiderman <talshn@mellanox.com>
> ---
>  lib/librte_mbuf/rte_mbuf_core.h | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
> index b9a59c879..82441555e 100644
> --- a/lib/librte_mbuf/rte_mbuf_core.h
> +++ b/lib/librte_mbuf/rte_mbuf_core.h
> @@ -521,11 +521,12 @@ struct rte_mbuf {
>  	RTE_STD_C11
>  	union {
>  		uint32_t packet_type; /**< L2/L3/L4 and tunnel information. */
> +		__extension__
>  		struct {
> -			uint32_t l2_type:4; /**< (Outer) L2 type. */
> -			uint32_t l3_type:4; /**< (Outer) L3 type. */
> -			uint32_t l4_type:4; /**< (Outer) L4 type. */
> -			uint32_t tun_type:4; /**< Tunnel type. */
> +			uint8_t l2_type:4; /**< (Outer) L2 type. */
> +			uint8_t l3_type:4; /**< (Outer) L3 type. */
> +			uint8_t l4_type:4; /**< (Outer) L4 type. */
> +			uint8_t tun_type:4; /**< Tunnel type. */
>  			RTE_STD_C11
>  			union {
>  				uint8_t inner_esp_next_proto;
> @@ -541,7 +542,7 @@ struct rte_mbuf {
>  					/**< Inner L3 type. */
>  				};
>  			};
> -			uint32_t inner_l4_type:4; /**< Inner L4 type. */
> +			uint8_t inner_l4_type:4; /**< Inner L4 type. */
>  		};
>  	};