[PATCH v7 2/4] mbuf: remove rte marker fields

[Bruce Richardson]

On Wed, Mar 20, 2024 at 03:01:36PM -0700, Tyler Retzlaff wrote:
> RTE_MARKER typedefs are a GCC extension unsupported by MSVC. Remove
> RTE_MARKER fields from rte_mbuf struct.
> 
> Maintain alignment of fields after removed cacheline1 marker by placing
> C11 alignas(RTE_CACHE_LINE_MIN_SIZE).
> 
> Provide new rearm_data and rx_descriptor_fields1 fields in anonymous
> unions as single element arrays of with types matching the original
> markers to maintain API compatibility.
> 
> Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> ---
>  doc/guides/rel_notes/release_24_03.rst |   2 +
>  lib/mbuf/rte_mbuf.h                    |   4 +-
>  lib/mbuf/rte_mbuf_core.h               | 188 ++++++++++++++++++---------------
>  3 files changed, 104 insertions(+), 90 deletions(-)
> 
> diff --git a/doc/guides/rel_notes/release_24_03.rst b/doc/guides/rel_notes/release_24_03.rst
> index 14826ea..4f18cca 100644
> --- a/doc/guides/rel_notes/release_24_03.rst
> +++ b/doc/guides/rel_notes/release_24_03.rst
> @@ -216,6 +216,8 @@ Removed Items
>  
>  * acc101: Removed obsolete code for non productized HW variant.
>  
> +* mbuf: ``RTE_MARKER`` fields ``cacheline0`` and ``cacheline1``
> +  have been removed from ``struct rte_mbuf``.
>  
>  API Changes
>  -----------
> diff --git a/lib/mbuf/rte_mbuf.h b/lib/mbuf/rte_mbuf.h
> index 286b32b..4c4722e 100644
> --- a/lib/mbuf/rte_mbuf.h
> +++ b/lib/mbuf/rte_mbuf.h
> @@ -108,7 +108,7 @@
>  static inline void
>  rte_mbuf_prefetch_part1(struct rte_mbuf *m)
>  {
> -	rte_prefetch0(&m->cacheline0);
> +	rte_prefetch0(m);
>  }
>  
>  /**
> @@ -126,7 +126,7 @@
>  rte_mbuf_prefetch_part2(struct rte_mbuf *m)
>  {
>  #if RTE_CACHE_LINE_SIZE == 64
> -	rte_prefetch0(&m->cacheline1);
> +	rte_prefetch0(RTE_PTR_ADD(m, RTE_CACHE_LINE_MIN_SIZE));
>  #else
>  	RTE_SET_USED(m);
>  #endif
> diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
> index 9f58076..665213c 100644
> --- a/lib/mbuf/rte_mbuf_core.h
> +++ b/lib/mbuf/rte_mbuf_core.h
> @@ -465,8 +465,6 @@ enum {
>   * The generic rte_mbuf, containing a packet mbuf.
>   */
>  struct __rte_cache_aligned rte_mbuf {
> -	RTE_MARKER cacheline0;
> -
>  	void *buf_addr;           /**< Virtual address of segment buffer. */
>  #if RTE_IOVA_IN_MBUF
>  	/**
> @@ -488,116 +486,130 @@ struct __rte_cache_aligned rte_mbuf {
>  #endif
>  
>  	/* next 8 bytes are initialised on RX descriptor rearm */
> -	RTE_MARKER64 rearm_data;
> -	uint16_t data_off;
> -
> -	/**
> -	 * Reference counter. Its size should at least equal to the size
> -	 * of port field (16 bits), to support zero-copy broadcast.
> -	 * It should only be accessed using the following functions:
> -	 * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
> -	 * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
> -	 * or non-atomic) is controlled by the RTE_MBUF_REFCNT_ATOMIC flag.
> -	 */
> -	RTE_ATOMIC(uint16_t) refcnt;
> +	union {
> +		uint64_t rearm_data[1];
> +		__extension__
> +		struct {
> +			uint16_t data_off;
> +
> +			/**
> +			 * Reference counter. Its size should at least equal to the size
> +			 * of port field (16 bits), to support zero-copy broadcast.
> +			 * It should only be accessed using the following functions:
> +			 * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
> +			 * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
> +			 * or non-atomic) is controlled by the RTE_MBUF_REFCNT_ATOMIC flag.
> +			 */
> +			RTE_ATOMIC(uint16_t) refcnt;
>  
> -	/**
> -	 * Number of segments. Only valid for the first segment of an mbuf
> -	 * chain.
> -	 */
> -	uint16_t nb_segs;
> +			/**
> +			 * Number of segments. Only valid for the first segment of an mbuf
> +			 * chain.
> +			 */
> +			uint16_t nb_segs;
>  
> -	/** Input port (16 bits to support more than 256 virtual ports).
> -	 * The event eth Tx adapter uses this field to specify the output port.
> -	 */
> -	uint16_t port;
> +			/** Input port (16 bits to support more than 256 virtual ports).
> +			 * The event eth Tx adapter uses this field to specify the output port.
> +			 */
> +			uint16_t port;
> +		};
> +	};
>  
>  	uint64_t ol_flags;        /**< Offload features. */
>  
>  	/* remaining bytes are set on RX when pulling packet from descriptor */
> -	RTE_MARKER rx_descriptor_fields1;
> -
> -	/*
> -	 * The packet type, which is the combination of outer/inner L2, L3, L4
> -	 * and tunnel types. The packet_type is about data really present in the
> -	 * mbuf. Example: if vlan stripping is enabled, a received vlan packet
> -	 * would have RTE_PTYPE_L2_ETHER and not RTE_PTYPE_L2_VLAN because the
> -	 * vlan is stripped from the data.
> -	 */
>  	union {
> -		uint32_t packet_type; /**< L2/L3/L4 and tunnel information. */
> +		void *rx_descriptor_fields1[1];

Can we make this array the actual size of all the fields, rather than just
an 8-byte value? That would allow the right think to be done if assigning
the descriptor fields from one mbuf to another, or when using memset or
memcpy on them.

/Bruce