RE: [PATCH 6/6] mempool: no cache size limit

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> Replaced the fixed size object array in the per-lcore local cache
> with a variable size array, allocated at mempool creation.
> For faster indexing into the per-lcore array of caches, pre-calculate
> the size (in bytes) of the per-lcore local cache.
> 
> Using a variable size array makes the RTE_MEMPOOL_CACHE_MAX_SIZE build
> time configuration parameter superfluous,
> but it was kept for compatibility purposes, as it is often used for
> the cache_size parameter when creating mempools.
> 
> Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> ---
> Supersedes: patch-169235
> ("[v2] mempool: no cache size limit")
> ---
>  app/test/test_mempool.c                |   2 +-
>  doc/guides/rel_notes/release_26_11.rst |  12 ++-
>  lib/mempool/rte_mempool.c              | 118 ++++++++++++++-----------
>  lib/mempool/rte_mempool.h              |  17 ++--
>  4 files changed, 86 insertions(+), 63 deletions(-)
> 
> diff --git a/app/test/test_mempool.c b/app/test/test_mempool.c
> index 6ff8746474..8a21b385d9 100644
> --- a/app/test/test_mempool.c
> +++ b/app/test/test_mempool.c
> @@ -193,7 +193,7 @@ static int
> test_mempool_creation_with_exceeded_cache_size(void)
>  	mp_cov = rte_mempool_create("test_cache_too_big",
>  		MEMPOOL_SIZE,
>  		MEMPOOL_ELT_SIZE,
> -		RTE_MEMPOOL_CACHE_MAX_SIZE + 32, 0,
> +		MEMPOOL_SIZE + 32, 0,
>  		NULL, NULL,
>  		my_obj_init, NULL,
>  		SOCKET_ID_ANY, 0);
> diff --git a/doc/guides/rel_notes/release_26_11.rst
> b/doc/guides/rel_notes/release_26_11.rst
> index 59b8514360..64f6802e58 100644
> --- a/doc/guides/rel_notes/release_26_11.rst
> +++ b/doc/guides/rel_notes/release_26_11.rst
> @@ -97,10 +97,20 @@ API Changes
>     Also, make sure to start the actual text at the margin.
>     =======================================================
> 
> +* mempool: When creating a mempool, the cache size can be freely specified
> +  (although still not exceed the number of elements),
> +  and is no longer limited by the ``RTE_MEMPOOL_CACHE_MAX_SIZE`` build time
> configuration parameter.
> +  Although ``RTE_MEMPOOL_CACHE_MAX_SIZE`` has lost its original meaning,
> +  it was kept for compatibility purposes,
> +  as it is often used for the ``cache_size`` parameter when creating mempools.
> +
> +* mempool: Updated the ``rte_mempool`` structure as follows:
> +  - Added the ``sizeof_cache_per_lcore`` field, for indexing into the per-lcore
> local cache.
> +
>  * mempool: Updated the ``rte_mempool_cache`` structure as follows:
>    - Removed the deprecated and obsolete ``flushthresh`` field.
>    - Removed the ``unused`` field.
> -  - Reduced the size of the ``objs`` array from
> ``RTE_MEMPOOL_CACHE_MAX_SIZE`` * 2 to
> ``RTE_MEMPOOL_CACHE_MAX_SIZE``.
> +  - Changed the ``objs`` array from fixed size to variable size.
> 
>  ABI Changes
>  -----------
> diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> index 211763aced..069aabaa70 100644
> --- a/lib/mempool/rte_mempool.c
> +++ b/lib/mempool/rte_mempool.c
> @@ -759,20 +759,21 @@ mempool_cache_init(struct rte_mempool_cache
> *cache, uint32_t size)
>  /*
>   * Create and initialize a cache for objects that are retrieved from and
>   * returned to an underlying mempool. This structure is identical to the
> - * local_cache[lcore_id] pointed to by the mempool structure.
> + * local_cache entry pointed to by the mempool structure.
>   */
>  RTE_EXPORT_SYMBOL(rte_mempool_cache_create)
>  struct rte_mempool_cache *
>  rte_mempool_cache_create(uint32_t size, int socket_id)
>  {
>  	struct rte_mempool_cache *cache;
> +	size_t sizeof_cache = sizeof(struct rte_mempool_cache) + size *
> sizeof(void *);
> 
> -	if (size == 0 || size > RTE_MEMPOOL_CACHE_MAX_SIZE) {
> +	if (size == 0 || sizeof_cache > UINT32_MAX) {
>  		rte_errno = EINVAL;
>  		return NULL;
>  	}
> 
> -	cache = rte_zmalloc_socket("MEMPOOL_CACHE", sizeof(*cache),
> +	cache = rte_zmalloc_socket("MEMPOOL_CACHE", sizeof_cache,
>  				  RTE_CACHE_LINE_SIZE, socket_id);
>  	if (cache == NULL) {
>  		RTE_MEMPOOL_LOG(ERR, "Cannot allocate mempool cache.");
> @@ -811,10 +812,9 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
>  	struct rte_mempool *mp = NULL;
>  	struct rte_tailq_entry *te = NULL;
>  	const struct rte_memzone *mz = NULL;
> -	size_t mempool_size;
> +	size_t mempool_size, sizeof_cache_per_lcore;
>  	unsigned int mz_flags =
> RTE_MEMZONE_1GB|RTE_MEMZONE_SIZE_HINT_ONLY;
>  	struct rte_mempool_objsz objsz;
> -	unsigned lcore_id;
>  	int ret;
> 
>  	/* compilation-time checks */
> @@ -822,6 +822,8 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
>  			  RTE_CACHE_LINE_MASK) != 0);
>  	RTE_BUILD_BUG_ON((sizeof(struct rte_mempool_cache) &
>  			  RTE_CACHE_LINE_MASK) != 0);
> +	RTE_BUILD_BUG_ON(offsetof(struct rte_mempool_cache, objs) !=
> +			  sizeof(struct rte_mempool_cache));
>  #ifdef RTE_LIBRTE_MEMPOOL_STATS
>  	RTE_BUILD_BUG_ON((sizeof(struct rte_mempool_debug_stats) &
>  			  RTE_CACHE_LINE_MASK) != 0);
> @@ -838,7 +840,18 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
>  	}
> 
>  	/* asked cache too big */
> -	if (cache_size > RTE_MEMPOOL_CACHE_MAX_SIZE ||
> +	sizeof_cache_per_lcore = 0;
> +	if (cache_size != 0) {
> +		sizeof_cache_per_lcore = sizeof(struct rte_mempool_cache);
> +		sizeof_cache_per_lcore +=
> RTE_CACHE_LINE_ROUNDUP(cache_size * sizeof(void *));
> +		/*
> +		 * Add padding, to guard against false sharing-like effects
> +		 * on systems with a next-N-lines hardware prefetcher, when
> +		 * accessing objects at the end of the cache.
> +		 */
> +		sizeof_cache_per_lcore += RTE_CACHE_GUARD_LINES *
> RTE_CACHE_LINE_SIZE;
> +	}
> +	if (sizeof_cache_per_lcore > UINT32_MAX ||
>  	    cache_size > n) {
>  		rte_errno = EINVAL;
>  		return NULL;
> @@ -890,8 +903,7 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
> 
>  	mempool_size = sizeof(struct rte_mempool);
>  	mempool_size += private_data_size;
> -	if (cache_size != 0)
> -		mempool_size += RTE_MAX_LCORE * sizeof(struct
> rte_mempool_cache);
> +	mempool_size += RTE_MAX_LCORE * sizeof_cache_per_lcore;
> 
>  	ret = snprintf(mz_name, sizeof(mz_name),
> RTE_MEMPOOL_MZ_FORMAT, name);
>  	if (ret < 0 || ret >= (int)sizeof(mz_name)) {
> @@ -918,7 +930,6 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
>  	mp->elt_size = objsz.elt_size;
>  	mp->header_size = objsz.header_size;
>  	mp->trailer_size = objsz.trailer_size;
> -	/* Size of default caches, zero means disabled. */
>  	mp->cache_size = cache_size;
>  	mp->private_data_size = private_data_size;
>  	STAILQ_INIT(&mp->elt_list);
> @@ -942,18 +953,17 @@ rte_mempool_create_empty(const char *name,
> unsigned n, unsigned elt_size,
>  		goto exit_unlock;
>  	}
> 
> -	/*
> -	 * local_cache pointer is set even if cache_size is zero.
> -	 * The local_cache points to just past the private data.
> -	 */
> -	mp->local_cache = (struct rte_mempool_cache *)
> -		RTE_PTR_ADD(mp, sizeof(struct rte_mempool) +
> private_data_size);
> -
> -	/* Init all default caches. */
> +	/* local_cache pointer is only set if per-lcore local cache is present */
>  	if (cache_size != 0) {
> -		for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
> -			mempool_cache_init(&mp->local_cache[lcore_id],
> -					   cache_size);
> +		mp->local_cache = (struct rte_mempool_cache *)
> +			RTE_PTR_ADD(mp, sizeof(struct rte_mempool) +
> private_data_size);
> +		mp->sizeof_cache_per_lcore = sizeof_cache_per_lcore;
> +
> +		/* Init all default caches. */
> +		struct rte_mempool_cache *cache = mp->local_cache;
> +		for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +				lcore_id++, cache = RTE_PTR_ADD(cache,
> sizeof_cache_per_lcore))
> +			mempool_cache_init(cache, cache_size);
>  	}
> 
>  	te->data = mp;
> @@ -1016,16 +1026,17 @@ RTE_EXPORT_SYMBOL(rte_mempool_avail_count)
>  unsigned int
>  rte_mempool_avail_count(const struct rte_mempool *mp)
>  {
> -	unsigned count;
> -	unsigned lcore_id;
> +	unsigned int count;
> 
>  	count = rte_mempool_ops_get_count(mp);
> 
> -	if (mp->cache_size == 0)
> +	if (mp->local_cache == NULL)
>  		return count;
> 
> -	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
> -		count += mp->local_cache[lcore_id].len;
> +	const struct rte_mempool_cache *cache = mp->local_cache;
> +	for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +			lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore))
> +		count += cache->len;
> 
>  	/*
>  	 * due to race condition (access to len is not locked), the
> @@ -1053,11 +1064,11 @@ rte_mempool_stats_reset(struct rte_mempool
> *mp)
> 
>  #ifdef RTE_LIBRTE_MEMPOOL_STATS
>  	memset(&mp->stats, 0, sizeof(mp->stats));
> -	if (mp->cache_size != 0) {
> -		for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> lcore_id++) {
> -			memset(&mp->local_cache[lcore_id].stats, 0,
> -					sizeof(mp->local_cache[lcore_id].stats));
> -		}
> +	if (mp->local_cache != NULL) {
> +		struct rte_mempool_cache *cache = mp->local_cache;
> +		for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +				lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore))
> +			memset(&cache->stats, 0, sizeof(cache->stats));
>  	}
> 
>  	RTE_MEMPOOL_LOG(DEBUG, "<%s>@%p: statistics reset", mp->name,
> mp);
> @@ -1071,18 +1082,18 @@ rte_mempool_stats_reset(struct rte_mempool
> *mp)
>  static unsigned
>  rte_mempool_dump_cache(FILE *f, const struct rte_mempool *mp)
>  {
> -	unsigned lcore_id;
> -	unsigned count = 0;
> -	unsigned cache_count;
> +	unsigned int count = 0;
> 
>  	fprintf(f, "  internal cache infos (hide zero value items):\n");
>  	fprintf(f, "    cache_size=%"PRIu32"\n", mp->cache_size);
> 
> -	if (mp->cache_size == 0)
> +	if (mp->local_cache == NULL)
>  		return count;
> 
> -	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
> -		cache_count = mp->local_cache[lcore_id].len;
> +	const struct rte_mempool_cache *cache = mp->local_cache;
> +	for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +			lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore)) {
> +		unsigned int cache_count = cache->len;
>  		if (cache_count == 0)
>  			continue;
>  		fprintf(f, "    cache_count[%u]=%"PRIu32"\n",
> @@ -1223,15 +1234,13 @@ mempool_audit_cookies(struct rte_mempool *mp)
>  static void
>  mempool_audit_cache(const struct rte_mempool *mp)
>  {
> -	unsigned lcore_id;
> -
> -	if (mp->cache_size == 0)
> +	if (mp->local_cache == NULL)
>  		return;
> 
> -	for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
> -		const struct rte_mempool_cache *cache;
> -		cache = &mp->local_cache[lcore_id];
> -		if (cache->size > RTE_DIM(cache->objs)) {
> +	const struct rte_mempool_cache *cache = mp->local_cache;
> +	for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +			lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore)) {
> +		if (cache->size > mp->size) {
>  			RTE_MEMPOOL_LOG(CRIT, "badness on cache[%u] size",
> lcore_id);
>  			rte_panic("MEMPOOL: invalid cache[%u] size\n",
> lcore_id);
>  		}
> @@ -1324,13 +1333,15 @@ rte_mempool_dump(FILE *f, struct rte_mempool
> *mp)
>  		sum.get_success_blks += mp->stats[lcore_id].get_success_blks;
>  		sum.get_fail_blks += mp->stats[lcore_id].get_fail_blks;
>  	}
> -	if (mp->cache_size != 0) {
> +	if (mp->local_cache != NULL) {
>  		/* Add the statistics stored in the mempool caches. */
> -		for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++) {
> -			sum.put_bulk += mp-
> >local_cache[lcore_id].stats.put_bulk;
> -			sum.put_objs += mp-
> >local_cache[lcore_id].stats.put_objs;
> -			sum.get_success_bulk += mp-
> >local_cache[lcore_id].stats.get_success_bulk;
> -			sum.get_success_objs += mp-
> >local_cache[lcore_id].stats.get_success_objs;
> +		const struct rte_mempool_cache *cache = mp->local_cache;
> +		for (lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +			lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore)) {
> +			sum.put_bulk += cache->stats.put_bulk;
> +			sum.put_objs += cache->stats.put_objs;
> +			sum.get_success_bulk += cache->stats.get_success_bulk;
> +			sum.get_success_objs += cache->stats.get_success_objs;
>  		}
>  	}
>  	fprintf(f, "  stats:\n");
> @@ -1627,10 +1638,11 @@ mempool_info_cb(struct rte_mempool *mp, void
> *arg)
>  				  mp->populated_size);
> 
>  	cache_count = 0;
> -	if (mp->cache_size > 0) {
> -		int lcore_id;
> -		for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
> -			cache_count += mp->local_cache[lcore_id].len;
> +	if (mp->local_cache != NULL) {
> +		const struct rte_mempool_cache *cache = mp->local_cache;
> +		for (unsigned int lcore_id = 0; lcore_id < RTE_MAX_LCORE;
> +				lcore_id++, cache = RTE_PTR_ADD(cache, mp-
> >sizeof_cache_per_lcore))
> +			cache_count += cache->len;
>  	}
>  	rte_tel_data_add_dict_uint(info->d, "total_cache_count", cache_count);
>  	common_count = rte_mempool_ops_get_count(mp);
> diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> index 5a81e53a9f..5fc7cdb79c 100644
> --- a/lib/mempool/rte_mempool.h
> +++ b/lib/mempool/rte_mempool.h
> @@ -105,8 +105,7 @@ struct __rte_cache_aligned rte_mempool_cache {
>  	} stats;                        /**< Statistics */
>  #endif
>  	/** Cache objects */
> -	alignas(RTE_CACHE_LINE_SIZE) void
> *objs[RTE_MEMPOOL_CACHE_MAX_SIZE];
> -	RTE_CACHE_GUARD;
> +	alignas(RTE_CACHE_LINE_SIZE) void *objs[];
>  };
> 
>  /**
> @@ -265,6 +264,7 @@ struct __rte_cache_aligned rte_mempool {
>  	int32_t ops_index;
> 
>  	struct rte_mempool_cache *local_cache; /**< Per-lcore local cache */
> +	uint32_t sizeof_cache_per_lcore; /**< Multiplier for indexing into the
> local cache. */
> 
>  	uint32_t populated_size;         /**< Number of populated objects. */
>  	struct rte_mempool_objhdr_list elt_list; /**< List of objects in pool */
> @@ -1050,8 +1050,7 @@ rte_mempool_free(struct rte_mempool *mp);
>   * @param cache_size
>   *   If cache_size is non-zero, the rte_mempool library will try to
>   *   limit the accesses to the common lockless pool, by maintaining a
> - *   per-lcore object cache. This argument must be lower or equal to
> - *   RTE_MEMPOOL_CACHE_MAX_SIZE and n.
> + *   per-lcore object cache. This argument must be lower or equal to n.
>   *   The access to the per-lcore table is of course
>   *   faster than the multi-producer/consumer pool. The cache can be
>   *   disabled if the cache_size argument is set to 0; it can be useful to
> @@ -1371,15 +1370,17 @@ rte_mempool_cache_create(uint32_t size, int
> socket_id)
>  static __rte_always_inline struct rte_mempool_cache *
>  rte_mempool_default_cache(struct rte_mempool *mp, unsigned lcore_id)
>  {
> -	if (unlikely(mp->cache_size == 0))
> +	if (unlikely(mp->local_cache == NULL))
>  		return NULL;
> 
>  	if (unlikely(lcore_id == LCORE_ID_ANY))
>  		return NULL;
> 
> -	rte_mempool_trace_default_cache(mp, lcore_id,
> -		&mp->local_cache[lcore_id]);
> -	return &mp->local_cache[lcore_id];
> +	struct rte_mempool_cache *cache = (struct rte_mempool_cache
> *)RTE_PTR_ADD(mp->local_cache,
> +			lcore_id * (size_t)mp->sizeof_cache_per_lcore);
> +	rte_mempool_trace_default_cache(mp, lcore_id, cache);
> +	__rte_assume(cache != NULL);
> +	return cache;
>  }
> 
>  /**
> --
> 2.43.0