Re: [dpdk-dev] [RFC] mempool: implement index-based per core cache

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> Current mempool per core cache implementation is based on pointer
> For most architectures, each pointer consumes 64b
> Replace it with index-based implementation, where in each buffer
> is addressed by (pool address + index)

I don't think it is going to work:
On 64-bit systems difference between pool address and it's elem address
could be bigger than 4GB.
 
> It will reduce memory requirements
> 
> L3Fwd performance testing reveals minor improvements in the cache
> performance and no change in throughput
> 
> Micro-benchmarking the patch using mempool_perf_test shows
> significant improvement with majority of the test cases
> 
> Future plan involves replacing global pool's pointer-based implementation with index-based implementation
> 
> Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
> ---
>  drivers/mempool/ring/rte_mempool_ring.c |  2 +-
>  lib/mempool/rte_mempool.c               |  8 +++
>  lib/mempool/rte_mempool.h               | 74 ++++++++++++++++++++++---
>  3 files changed, 74 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/mempool/ring/rte_mempool_ring.c b/drivers/mempool/ring/rte_mempool_ring.c
> index b1f09ff28f4d..e55913e47f21 100644
> --- a/drivers/mempool/ring/rte_mempool_ring.c
> +++ b/drivers/mempool/ring/rte_mempool_ring.c
> @@ -101,7 +101,7 @@ ring_alloc(struct rte_mempool *mp, uint32_t rg_flags)
>  		return -rte_errno;
> 
>  	mp->pool_data = r;
> -
> +	mp->local_cache_base_addr = &r[1];
>  	return 0;
>  }
> 
> diff --git a/lib/mempool/rte_mempool.c b/lib/mempool/rte_mempool.c
> index 59a588425bd6..424bdb19c323 100644
> --- a/lib/mempool/rte_mempool.c
> +++ b/lib/mempool/rte_mempool.c
> @@ -480,6 +480,7 @@ rte_mempool_populate_default(struct rte_mempool *mp)
>  	int ret;
>  	bool need_iova_contig_obj;
>  	size_t max_alloc_size = SIZE_MAX;
> +	unsigned lcore_id;
> 
>  	ret = mempool_ops_alloc_once(mp);
>  	if (ret != 0)
> @@ -600,6 +601,13 @@ rte_mempool_populate_default(struct rte_mempool *mp)
>  		}
>  	}
> 
> +	/* Init all default caches. */
> +	if (mp->cache_size != 0) {
> +		for (lcore_id = 0; lcore_id < RTE_MAX_LCORE; lcore_id++)
> +			mp->local_cache[lcore_id].local_cache_base_value =
> +				*(void **)mp->local_cache_base_addr;
> +	}
> +
>  	rte_mempool_trace_populate_default(mp);
>  	return mp->size;
> 
> diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
> index 4235d6f0bf2b..545405c0d3ce 100644
> --- a/lib/mempool/rte_mempool.h
> +++ b/lib/mempool/rte_mempool.h
> @@ -51,6 +51,8 @@
>  #include <rte_memcpy.h>
>  #include <rte_common.h>
> 
> +#include <arm_neon.h>
> +
>  #include "rte_mempool_trace_fp.h"
> 
>  #ifdef __cplusplus
> @@ -91,11 +93,12 @@ struct 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 */
> +	void *local_cache_base_value; /**< Base value to calculate indices */
>  	/*
>  	 * 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 * 3]; /**< Cache objects */
> +	uint32_t objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 3]; /**< Cache objects */
>  } __rte_cache_aligned;
> 
>  /**
> @@ -172,7 +175,6 @@ struct rte_mempool_objtlr {
>   * A list of memory where objects are stored
>   */
>  STAILQ_HEAD(rte_mempool_memhdr_list, rte_mempool_memhdr);
> -
>  /**
>   * Callback used to free a memory chunk
>   */
> @@ -244,6 +246,7 @@ struct rte_mempool {
>  	int32_t ops_index;
> 
>  	struct rte_mempool_cache *local_cache; /**< Per-lcore local cache */
> +	void *local_cache_base_addr; /**< Reference to the base value */
> 
>  	uint32_t populated_size;         /**< Number of populated objects. */
>  	struct rte_mempool_objhdr_list elt_list; /**< List of objects in pool */
> @@ -1269,7 +1272,15 @@ rte_mempool_cache_flush(struct rte_mempool_cache *cache,
>  	if (cache == NULL || cache->len == 0)
>  		return;
>  	rte_mempool_trace_cache_flush(cache, mp);
> -	rte_mempool_ops_enqueue_bulk(mp, cache->objs, cache->len);
> +
> +	unsigned int i;
> +	unsigned int cache_len = cache->len;
> +	void *obj_table[RTE_MEMPOOL_CACHE_MAX_SIZE * 3];
> +	void *base_value = cache->local_cache_base_value;
> +	uint32_t *cache_objs = cache->objs;
> +	for (i = 0; i < cache_len; i++)
> +		obj_table[i] = (void *) RTE_PTR_ADD(base_value, cache_objs[i]);
> +	rte_mempool_ops_enqueue_bulk(mp, obj_table, cache->len);
>  	cache->len = 0;
>  }
> 
> @@ -1289,7 +1300,9 @@ static __rte_always_inline void
>  __mempool_generic_put(struct rte_mempool *mp, void * const *obj_table,
>  		      unsigned int n, struct rte_mempool_cache *cache)
>  {
> -	void **cache_objs;
> +	uint32_t *cache_objs;
> +	void *base_value;
> +	uint32_t i;
> 
>  	/* increment stat now, adding in mempool always success */
>  	__MEMPOOL_STAT_ADD(mp, put_bulk, 1);
> @@ -1301,6 +1314,12 @@ __mempool_generic_put(struct rte_mempool *mp, void * const *obj_table,
> 
>  	cache_objs = &cache->objs[cache->len];
> 
> +	base_value = cache->local_cache_base_value;
> +
> +	uint64x2_t v_obj_table;
> +	uint64x2_t v_base_value = vdupq_n_u64((uint64_t)base_value);
> +	uint32x2_t v_cache_objs;
> +
>  	/*
>  	 * The cache follows the following algorithm
>  	 *   1. Add the objects to the cache
> @@ -1309,12 +1328,26 @@ __mempool_generic_put(struct rte_mempool *mp, void * const *obj_table,
>  	 */
> 
>  	/* Add elements back into the cache */
> -	rte_memcpy(&cache_objs[0], obj_table, sizeof(void *) * n);
> +
> +#if defined __ARM_NEON
> +	for (i = 0; i < (n & ~0x1); i+=2) {
> +		v_obj_table = vld1q_u64((const uint64_t *)&obj_table[i]);
> +		v_cache_objs = vqmovn_u64(vsubq_u64(v_obj_table, v_base_value));
> +		vst1_u32(cache_objs + i, v_cache_objs);
> +	}
> +	if (n & 0x1) {
> +		cache_objs[i] = (uint32_t) RTE_PTR_DIFF(obj_table[i], base_value);
> +	}
> +#else
> +	for (i = 0; i < n; i++) {
> +		cache_objs[i] = (uint32_t) RTE_PTR_DIFF(obj_table[i], base_value);
> +	}
> +#endif
> 
>  	cache->len += n;
> 
>  	if (cache->len >= cache->flushthresh) {
> -		rte_mempool_ops_enqueue_bulk(mp, &cache->objs[cache->size],
> +		rte_mempool_ops_enqueue_bulk(mp, obj_table + cache->len - cache->size,
>  				cache->len - cache->size);
>  		cache->len = cache->size;
>  	}
> @@ -1415,23 +1448,26 @@ __mempool_generic_get(struct rte_mempool *mp, void **obj_table,
>  		      unsigned int n, struct rte_mempool_cache *cache)
>  {
>  	int ret;
> +	uint32_t i;
>  	uint32_t index, len;
> -	void **cache_objs;
> +	uint32_t *cache_objs;
> 
>  	/* No cache provided or cannot be satisfied from cache */
>  	if (unlikely(cache == NULL || n >= cache->size))
>  		goto ring_dequeue;
> 
> +	void *base_value = cache->local_cache_base_value;
>  	cache_objs = cache->objs;
> 
>  	/* Can this be satisfied from the cache? */
>  	if (cache->len < n) {
>  		/* No. Backfill the cache first, and then fill from it */
>  		uint32_t req = n + (cache->size - cache->len);
> +		void *temp_objs[RTE_MEMPOOL_CACHE_MAX_SIZE * 3]; /**< Cache objects */
> 
>  		/* How many do we require i.e. number to fill the cache + the request */
>  		ret = rte_mempool_ops_dequeue_bulk(mp,
> -			&cache->objs[cache->len], req);
> +			temp_objs, req);
>  		if (unlikely(ret < 0)) {
>  			/*
>  			 * In the off chance that we are buffer constrained,
> @@ -1442,12 +1478,32 @@ __mempool_generic_get(struct rte_mempool *mp, void **obj_table,
>  			goto ring_dequeue;
>  		}
> 
> +		len = cache->len;
> +		for (i = 0; i < req; ++i, ++len) {
> +			cache_objs[len] = (uint32_t) RTE_PTR_DIFF(temp_objs[i], base_value);
> +		}
> +
>  		cache->len += req;
>  	}
> 
> +	uint64x2_t v_obj_table;
> +	uint64x2_t v_cache_objs;
> +	uint64x2_t v_base_value = vdupq_n_u64((uint64_t)base_value);
> +
>  	/* Now fill in the response ... */
> +#if defined __ARM_NEON
> +	for (index = 0, len = cache->len - 1; index < (n & ~0x1); index+=2,
> +						len-=2, obj_table+=2) {
> +		v_cache_objs = vmovl_u32(vld1_u32(cache_objs + len - 1));
> +		v_obj_table = vaddq_u64(v_cache_objs, v_base_value);
> +		vst1q_u64((uint64_t *)obj_table, v_obj_table);
> +	}
> +	if (n & 0x1)
> +		*obj_table = (void *) RTE_PTR_ADD(base_value, cache_objs[len]);
> +#else
>  	for (index = 0, len = cache->len - 1; index < n; ++index, len--, obj_table++)
> -		*obj_table = cache_objs[len];
> +		*obj_table = (void *) RTE_PTR_ADD(base_value, cache_objs[len]);
> +#endif
> 
>  	cache->len -= n;
> 
> --
> 2.17.1