[PATCH v6 27/39] mempool: use C11 alignas

[Konstantin Ananyev]

> Subject: [PATCH v6 27/39] mempool: use C11 alignas
> 
> The current location used for __rte_aligned(a) for alignment of types
> and variables is not compatible with MSVC. There is only a single
> location accepted by both toolchains.
> 
> For variables standard C11 offers alignas(a) supported by conformant
> compilers i.e. both MSVC and GCC.
> 
> For types the standard offers no alignment facility that compatibly
> interoperates with C and C++ but may be achieved by relocating the
> placement of __rte_aligned(a) to the aforementioned location accepted
> by all currently supported toolchains.
> 
> To allow alignment for both compilers do the following:
> 
> * Move __rte_aligned from the end of {struct,union} definitions to
>   be between {struct,union} and tag.
> 
>   The placement between {struct,union} and the tag allows the desired
>   alignment to be imparted on the type regardless of the toolchain being
>   used for all of GCC, LLVM, MSVC compilers building both C and C++.
> 
> * Replace use of __rte_aligned(a) on variables/fields with alignas(a).
> 
> Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> Acked-by: Morten Brørup <mb at smartsharesystems.com>
> ---
>  lib/mempool/rte_mempool.h | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> index 6fa4d48..23fd5c8 100644
> --- a/lib/mempool/rte_mempool.h
> +++ b/lib/mempool/rte_mempool.h
> @@ -34,6 +34,7 @@
>   * user cache created with rte_mempool_cache_create().
>   */
> 
> +#include <stdalign.h>
>  #include <stdio.h>
>  #include <stdint.h>
>  #include <inttypes.h>
> @@ -66,7 +67,7 @@
>   * captured since they can be calculated from other stats.
>   * For example: put_cache_objs = put_objs - put_common_pool_objs.
>   */
> -struct rte_mempool_debug_stats {
> +struct __rte_cache_aligned rte_mempool_debug_stats {
>  	uint64_t put_bulk;             /**< Number of puts. */
>  	uint64_t put_objs;             /**< Number of objects successfully put. */
>  	uint64_t put_common_pool_bulk; /**< Number of bulks enqueued in common pool. */
> @@ -80,13 +81,13 @@ struct rte_mempool_debug_stats {
>  	uint64_t get_success_blks;     /**< Successful allocation number of contiguous blocks. */
>  	uint64_t get_fail_blks;        /**< Failed allocation number of contiguous blocks. */
>  	RTE_CACHE_GUARD;
> -} __rte_cache_aligned;
> +};
>  #endif
> 
>  /**
>   * A structure that stores a per-core object cache.
>   */
> -struct rte_mempool_cache {
> +struct __rte_cache_aligned rte_mempool_cache {
>  	uint32_t size;	      /**< Size of the cache */
>  	uint32_t flushthresh; /**< Threshold before we flush excess elements */
>  	uint32_t len;	      /**< Current cache count */
> @@ -109,8 +110,8 @@ struct rte_mempool_cache {
>  	 * Cache is allocated to this size to allow it to overflow in certain
>  	 * cases to avoid needless emptying of cache.
>  	 */
> -	void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 2] __rte_cache_aligned;
> -} __rte_cache_aligned;
> +	alignas(RTE_CACHE_LINE_SIZE) void *objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 2];
> +};
> 
>  /**
>   * A structure that stores the size of mempool elements.
> @@ -218,15 +219,15 @@ struct rte_mempool_memhdr {
>   * The structure is cache-line aligned to avoid ABI breakages in
>   * a number of cases when something small is added.
>   */
> -struct rte_mempool_info {
> +struct __rte_cache_aligned rte_mempool_info {
>  	/** Number of objects in the contiguous block */
>  	unsigned int contig_block_size;
> -} __rte_cache_aligned;
> +};
> 
>  /**
>   * The RTE mempool structure.
>   */
> -struct rte_mempool {
> +struct __rte_cache_aligned rte_mempool {
>  	char name[RTE_MEMPOOL_NAMESIZE]; /**< Name of mempool. */
>  	union {
>  		void *pool_data;         /**< Ring or pool to store objects. */
> @@ -268,7 +269,7 @@ struct rte_mempool {
>  	 */
>  	struct rte_mempool_debug_stats stats[RTE_MAX_LCORE + 1];
>  #endif
> -}  __rte_cache_aligned;
> +};
> 
>  /** Spreading among memory channels not required. */
>  #define RTE_MEMPOOL_F_NO_SPREAD		0x0001
> @@ -688,7 +689,7 @@ typedef int (*rte_mempool_get_info_t)(const struct rte_mempool *mp,
> 
> 
>  /** Structure defining mempool operations structure */
> -struct rte_mempool_ops {
> +struct __rte_cache_aligned rte_mempool_ops {
>  	char name[RTE_MEMPOOL_OPS_NAMESIZE]; /**< Name of mempool ops struct. */
>  	rte_mempool_alloc_t alloc;       /**< Allocate private data. */
>  	rte_mempool_free_t free;         /**< Free the external pool. */
> @@ -713,7 +714,7 @@ struct rte_mempool_ops {
>  	 * Dequeue a number of contiguous object blocks.
>  	 */
>  	rte_mempool_dequeue_contig_blocks_t dequeue_contig_blocks;
> -} __rte_cache_aligned;
> +};
> 
>  #define RTE_MEMPOOL_MAX_OPS_IDX 16  /**< Max registered ops structs */
> 
> @@ -726,14 +727,14 @@ struct rte_mempool_ops {
>   * any function pointers stored directly in the mempool struct would not be.
>   * This results in us simply having "ops_index" in the mempool struct.
>   */
> -struct rte_mempool_ops_table {
> +struct __rte_cache_aligned rte_mempool_ops_table {
>  	rte_spinlock_t sl;     /**< Spinlock for add/delete. */
>  	uint32_t num_ops;      /**< Number of used ops structs in the table. */
>  	/**
>  	 * Storage for all possible ops structs.
>  	 */
>  	struct rte_mempool_ops ops[RTE_MEMPOOL_MAX_OPS_IDX];
> -} __rte_cache_aligned;
> +};
> 
>  /** Array of registered ops structs. */
>  extern struct rte_mempool_ops_table rte_mempool_ops_table;
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev at huawei.com>

> 1.8.3.1