diff mbox series

[v4,4/4] hash: use partial-key hashing

Message ID 1538155426-145177-5-git-send-email-yipeng1.wang@intel.com (mailing list archive)
State Superseded, archived
Delegated to: Thomas Monjalon
Headers show
Series hash: add extendable bucket and partial key hashing | expand

Checks

Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Wang, Yipeng1 Sept. 28, 2018, 5:23 p.m. UTC
This commit changes the hashing mechanism to "partial-key
hashing" to calculate bucket index and signature of key.

This is  proposed in Bin Fan, et al's paper
"MemC3: Compact and Concurrent MemCache with Dumber Caching
and Smarter Hashing". Bascially the idea is to use "xor" to
derive alternative bucket from current bucket index and
signature.

With "partial-key hashing", it reduces the bucket memory
requirement from two cache lines to one cache line, which
improves the memory efficiency and thus the lookup speed.

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
---
 lib/librte_hash/rte_cuckoo_hash.c | 246 +++++++++++++++++++-------------------
 lib/librte_hash/rte_cuckoo_hash.h |   6 +-
 lib/librte_hash/rte_hash.h        |   5 +-
 3 files changed, 131 insertions(+), 126 deletions(-)

Comments

Honnappa Nagarahalli Oct. 1, 2018, 8:09 p.m. UTC | #1
> 
> This commit changes the hashing mechanism to "partial-key hashing" to
> calculate bucket index and signature of key.
> 
> This is  proposed in Bin Fan, et al's paper
> "MemC3: Compact and Concurrent MemCache with Dumber Caching and
> Smarter Hashing". Bascially the idea is to use "xor" to derive alternative
> bucket from current bucket index and signature.
> 
> With "partial-key hashing", it reduces the bucket memory requirement from
> two cache lines to one cache line, which improves the memory efficiency and
> thus the lookup speed.
> 
> Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
> ---
>  lib/librte_hash/rte_cuckoo_hash.c | 246 +++++++++++++++++++------------------
> -
>  lib/librte_hash/rte_cuckoo_hash.h |   6 +-
>  lib/librte_hash/rte_hash.h        |   5 +-
>  3 files changed, 131 insertions(+), 126 deletions(-)
> 
> diff --git a/lib/librte_hash/rte_cuckoo_hash.c
> b/lib/librte_hash/rte_cuckoo_hash.c
> index 02650b9..e101708 100644
> --- a/lib/librte_hash/rte_cuckoo_hash.c
> +++ b/lib/librte_hash/rte_cuckoo_hash.c
> @@ -90,6 +90,36 @@ rte_hash_cmp_eq(const void *key1, const void *key2,
> const struct rte_hash *h)
>  		return cmp_jump_table[h->cmp_jump_table_idx](key1, key2,
> h->key_len);  }
> 
> +/*
> + * We use higher 16 bits of hash as the signature value stored in table.
> + * We use the lower bits for the primary bucket
> + * location. Then we XOR primary bucket location and the signature
> + * to get the secondary bucket location. This is same as
> + * proposed in Bin Fan, et al's paper
> + * "MemC3: Compact and Concurrent MemCache with Dumber Caching and
> + * Smarter Hashing". The benefit to use
> + * XOR is that one could derive the alternative bucket location
> + * by only using the current bucket location and the signature.
> + */
> +static inline uint16_t
> +get_short_sig(const hash_sig_t hash)
> +{
> +	return hash >> 16;
> +}
> +
> +static inline uint32_t
> +get_prim_bucket_index(const struct rte_hash *h, const hash_sig_t hash)
> +{
> +	return hash & h->bucket_bitmask;
> +}
> +
> +static inline uint32_t
> +get_alt_bucket_index(const struct rte_hash *h,
> +			uint32_t cur_bkt_idx, uint16_t sig)
> +{
> +	return (cur_bkt_idx ^ sig) & h->bucket_bitmask; }
> +
>  struct rte_hash *
>  rte_hash_create(const struct rte_hash_parameters *params)  { @@ -327,9
> +357,7 @@ rte_hash_create(const struct rte_hash_parameters *params)
>  	h->ext_table_support = ext_table_support;
> 
>  #if defined(RTE_ARCH_X86)
> -	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX2))
> -		h->sig_cmp_fn = RTE_HASH_COMPARE_AVX2;
> -	else if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE2))
> +	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE2))
>  		h->sig_cmp_fn = RTE_HASH_COMPARE_SSE;
>  	else
>  #endif
> @@ -417,18 +445,6 @@ rte_hash_hash(const struct rte_hash *h, const void
> *key)
>  	return h->hash_func(key, h->key_len, h->hash_func_init_val);  }
> 
> -/* Calc the secondary hash value from the primary hash value of a given key
> */ -static inline hash_sig_t -rte_hash_secondary_hash(const hash_sig_t
> primary_hash) -{
> -	static const unsigned all_bits_shift = 12;
> -	static const unsigned alt_bits_xor = 0x5bd1e995;
> -
> -	uint32_t tag = primary_hash >> all_bits_shift;
> -
> -	return primary_hash ^ ((tag + 1) * alt_bits_xor);
> -}
> -
>  int32_t
>  rte_hash_count(const struct rte_hash *h)  { @@ -560,14 +576,13 @@
> enqueue_slot_back(const struct rte_hash *h,
>  /* Search a key from bucket and update its data */  static inline int32_t
> search_and_update(const struct rte_hash *h, void *data, const void *key,
> -	struct rte_hash_bucket *bkt, hash_sig_t sig, hash_sig_t alt_hash)
> +	struct rte_hash_bucket *bkt, uint16_t sig)
>  {
>  	int i;
>  	struct rte_hash_key *k, *keys = h->key_store;
> 
>  	for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
> -		if (bkt->sig_current[i] == sig &&
> -				bkt->sig_alt[i] == alt_hash) {
> +		if (bkt->sig_current[i] == sig) {
>  			k = (struct rte_hash_key *) ((char *)keys +
>  					bkt->key_idx[i] * h->key_entry_size);
>  			if (rte_hash_cmp_eq(key, k->key, h) == 0) { @@ -
> 594,7 +609,7 @@ rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
>  		struct rte_hash_bucket *prim_bkt,
>  		struct rte_hash_bucket *sec_bkt,
>  		const struct rte_hash_key *key, void *data,
> -		hash_sig_t sig, hash_sig_t alt_hash, uint32_t new_idx,
> +		uint16_t sig, uint32_t new_idx,
>  		int32_t *ret_val)
>  {
>  	unsigned int i;
> @@ -605,7 +620,7 @@ rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
>  	/* Check if key was inserted after last check but before this
>  	 * protected region in case of inserting duplicated keys.
>  	 */
> -	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
> +	ret = search_and_update(h, data, key, prim_bkt, sig);
>  	if (ret != -1) {
>  		__hash_rw_writer_unlock(h);
>  		*ret_val = ret;
> @@ -613,7 +628,7 @@ rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
>  	}
> 
>  	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
> -		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
> +		ret = search_and_update(h, data, key, cur_bkt, sig);
>  		if (ret != -1) {
>  			__hash_rw_writer_unlock(h);
>  			*ret_val = ret;
> @@ -628,7 +643,6 @@ rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
>  		/* Check if slot is available */
>  		if (likely(prim_bkt->key_idx[i] == EMPTY_SLOT)) {
>  			prim_bkt->sig_current[i] = sig;
> -			prim_bkt->sig_alt[i] = alt_hash;
>  			prim_bkt->key_idx[i] = new_idx;
>  			break;
>  		}
> @@ -653,7 +667,7 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  			struct rte_hash_bucket *alt_bkt,
>  			const struct rte_hash_key *key, void *data,
>  			struct queue_node *leaf, uint32_t leaf_slot,
> -			hash_sig_t sig, hash_sig_t alt_hash, uint32_t new_idx,
> +			uint16_t sig, uint32_t new_idx,
>  			int32_t *ret_val)
>  {
>  	uint32_t prev_alt_bkt_idx;
> @@ -674,7 +688,7 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  	/* Check if key was inserted after last check but before this
>  	 * protected region.
>  	 */
> -	ret = search_and_update(h, data, key, bkt, sig, alt_hash);
> +	ret = search_and_update(h, data, key, bkt, sig);
>  	if (ret != -1) {
>  		__hash_rw_writer_unlock(h);
>  		*ret_val = ret;
> @@ -682,7 +696,7 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  	}
> 
>  	FOR_EACH_BUCKET(cur_bkt, alt_bkt) {
> -		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
> +		ret = search_and_update(h, data, key, cur_bkt, sig);
>  		if (ret != -1) {
>  			__hash_rw_writer_unlock(h);
>  			*ret_val = ret;
> @@ -695,8 +709,9 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  		prev_bkt = prev_node->bkt;
>  		prev_slot = curr_node->prev_slot;
> 
> -		prev_alt_bkt_idx =
> -			prev_bkt->sig_alt[prev_slot] & h->bucket_bitmask;
> +		prev_alt_bkt_idx = get_alt_bucket_index(h,
> +					prev_node->cur_bkt_idx,
> +					prev_bkt->sig_current[prev_slot]);
> 
>  		if (unlikely(&h->buckets[prev_alt_bkt_idx]
>  				!= curr_bkt)) {
> @@ -710,10 +725,8 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  		 * Cuckoo insert to move elements back to its
>  		 * primary bucket if available
>  		 */
> -		curr_bkt->sig_alt[curr_slot] =
> -			 prev_bkt->sig_current[prev_slot];
>  		curr_bkt->sig_current[curr_slot] =
> -			prev_bkt->sig_alt[prev_slot];
> +			prev_bkt->sig_current[prev_slot];
>  		curr_bkt->key_idx[curr_slot] =
>  			prev_bkt->key_idx[prev_slot];
> 
> @@ -723,7 +736,6 @@ rte_hash_cuckoo_move_insert_mw(const struct
> rte_hash *h,
>  	}
> 
>  	curr_bkt->sig_current[curr_slot] = sig;
> -	curr_bkt->sig_alt[curr_slot] = alt_hash;
>  	curr_bkt->key_idx[curr_slot] = new_idx;
> 
>  	__hash_rw_writer_unlock(h);
> @@ -741,39 +753,44 @@ rte_hash_cuckoo_make_space_mw(const struct
> rte_hash *h,
>  			struct rte_hash_bucket *bkt,
>  			struct rte_hash_bucket *sec_bkt,
>  			const struct rte_hash_key *key, void *data,
> -			hash_sig_t sig, hash_sig_t alt_hash,
> +			uint16_t sig, uint32_t bucket_idx,
>  			uint32_t new_idx, int32_t *ret_val)
>  {
>  	unsigned int i;
>  	struct queue_node queue[RTE_HASH_BFS_QUEUE_MAX_LEN];
>  	struct queue_node *tail, *head;
>  	struct rte_hash_bucket *curr_bkt, *alt_bkt;
> +	uint32_t cur_idx, alt_idx;
> 
>  	tail = queue;
>  	head = queue + 1;
>  	tail->bkt = bkt;
>  	tail->prev = NULL;
>  	tail->prev_slot = -1;
> +	tail->cur_bkt_idx = bucket_idx;
> 
>  	/* Cuckoo bfs Search */
>  	while (likely(tail != head && head <
>  					queue +
> RTE_HASH_BFS_QUEUE_MAX_LEN -
>  					RTE_HASH_BUCKET_ENTRIES)) {
>  		curr_bkt = tail->bkt;
> +		cur_idx = tail->cur_bkt_idx;
>  		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
>  			if (curr_bkt->key_idx[i] == EMPTY_SLOT) {
>  				int32_t ret =
> rte_hash_cuckoo_move_insert_mw(h,
>  						bkt, sec_bkt, key, data,
> -						tail, i, sig, alt_hash,
> +						tail, i, sig,
>  						new_idx, ret_val);
>  				if (likely(ret != -1))
>  					return ret;
>  			}
> 
>  			/* Enqueue new node and keep prev node info */
> -			alt_bkt = &(h->buckets[curr_bkt->sig_alt[i]
> -						    & h->bucket_bitmask]);
> +			alt_idx = get_alt_bucket_index(h, cur_idx,
> +						curr_bkt->sig_current[i]);
> +			alt_bkt = &(h->buckets[alt_idx]);
>  			head->bkt = alt_bkt;
> +			head->cur_bkt_idx = alt_idx;
>  			head->prev = tail;
>  			head->prev_slot = i;
>  			head++;
> @@ -788,7 +805,7 @@ static inline int32_t
> __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
>  						hash_sig_t sig, void *data)
>  {
> -	hash_sig_t alt_hash;
> +	uint16_t short_sig;
>  	uint32_t prim_bucket_idx, sec_bucket_idx;
>  	struct rte_hash_bucket *prim_bkt, *sec_bkt, *cur_bkt;
>  	struct rte_hash_key *new_k, *keys = h->key_store; @@ -803,18
> +820,17 @@ __rte_hash_add_key_with_hash(const struct rte_hash *h, const
> void *key,
>  	int32_t ret_val;
>  	struct rte_hash_bucket *last;
> 
> -	prim_bucket_idx = sig & h->bucket_bitmask;
> +	short_sig = get_short_sig(sig);
> +	prim_bucket_idx = get_prim_bucket_index(h, sig);
> +	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
>  	prim_bkt = &h->buckets[prim_bucket_idx];
> -	rte_prefetch0(prim_bkt);
> -
> -	alt_hash = rte_hash_secondary_hash(sig);
> -	sec_bucket_idx = alt_hash & h->bucket_bitmask;
>  	sec_bkt = &h->buckets[sec_bucket_idx];
> +	rte_prefetch0(prim_bkt);
>  	rte_prefetch0(sec_bkt);
> 
>  	/* Check if key is already inserted in primary location */
>  	__hash_rw_writer_lock(h);
> -	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
> +	ret = search_and_update(h, data, key, prim_bkt, short_sig);
>  	if (ret != -1) {
>  		__hash_rw_writer_unlock(h);
>  		return ret;
> @@ -822,12 +838,13 @@ __rte_hash_add_key_with_hash(const struct
> rte_hash *h, const void *key,
> 
>  	/* Check if key is already inserted in secondary location */
>  	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
> -		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
> +		ret = search_and_update(h, data, key, cur_bkt, short_sig);
>  		if (ret != -1) {
>  			__hash_rw_writer_unlock(h);
>  			return ret;
>  		}
>  	}
> +
>  	__hash_rw_writer_unlock(h);
> 
>  	/* Did not find a match, so get a new slot for storing the new key */
> @@ -865,7 +882,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash
> *h, const void *key,
> 
>  	/* Find an empty slot and insert */
>  	ret = rte_hash_cuckoo_insert_mw(h, prim_bkt, sec_bkt, key, data,
> -					sig, alt_hash, new_idx, &ret_val);
> +					short_sig, new_idx, &ret_val);
>  	if (ret == 0)
>  		return new_idx - 1;
>  	else if (ret == 1) {
> @@ -875,7 +892,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash
> *h, const void *key,
> 
>  	/* Primary bucket full, need to make space for new entry */
>  	ret = rte_hash_cuckoo_make_space_mw(h, prim_bkt, sec_bkt, key,
> data,
> -					sig, alt_hash, new_idx, &ret_val);
> +				short_sig, prim_bucket_idx, new_idx,
> &ret_val);
>  	if (ret == 0)
>  		return new_idx - 1;
>  	else if (ret == 1) {
> @@ -885,7 +902,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash
> *h, const void *key,
> 
>  	/* Also search secondary bucket to get better occupancy */
>  	ret = rte_hash_cuckoo_make_space_mw(h, sec_bkt, prim_bkt, key,
> data,
> -					alt_hash, sig, new_idx, &ret_val);
> +				short_sig, sec_bucket_idx, new_idx, &ret_val);
> 
>  	if (ret == 0)
>  		return new_idx - 1;
> @@ -905,14 +922,14 @@ __rte_hash_add_key_with_hash(const struct
> rte_hash *h, const void *key,
>  	 */
>  	__hash_rw_writer_lock(h);
>  	/* We check for duplicates again since could be inserted before the
> lock */
> -	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
> +	ret = search_and_update(h, data, key, prim_bkt, short_sig);
>  	if (ret != -1) {
>  		enqueue_slot_back(h, cached_free_slots, slot_id);
>  		goto failure;
>  	}
> 
>  	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
> -		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
> +		ret = search_and_update(h, data, key, cur_bkt, short_sig);
>  		if (ret != -1) {
>  			enqueue_slot_back(h, cached_free_slots, slot_id);
>  			goto failure;
> @@ -924,8 +941,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash
> *h, const void *key,
>  		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
>  			/* Check if slot is available */
>  			if (likely(cur_bkt->key_idx[i] == EMPTY_SLOT)) {
> -				cur_bkt->sig_current[i] = alt_hash;
> -				cur_bkt->sig_alt[i] = sig;
> +				cur_bkt->sig_current[i] = short_sig;
>  				cur_bkt->key_idx[i] = new_idx;
>  				__hash_rw_writer_unlock(h);
>  				return new_idx - 1;
> @@ -943,8 +959,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash
> *h, const void *key,
> 
>  	bkt_id = (uint32_t)((uintptr_t)ext_bkt_id) - 1;
>  	/* Use the first location of the new bucket */
> -	(h->buckets_ext[bkt_id]).sig_current[0] = alt_hash;
> -	(h->buckets_ext[bkt_id]).sig_alt[0] = sig;
> +	(h->buckets_ext[bkt_id]).sig_current[0] = short_sig;
>  	(h->buckets_ext[bkt_id]).key_idx[0] = new_idx;
>  	/* Link the new bucket to sec bucket linked list */
>  	last = rte_hash_get_last_bkt(sec_bkt); @@ -1003,7 +1018,7 @@
> rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data)
> 
>  /* Search one bucket to find the match key */  static inline int32_t -
> search_one_bucket(const struct rte_hash *h, const void *key, hash_sig_t sig,
> +search_one_bucket(const struct rte_hash *h, const void *key, uint16_t
> +sig,
>  			void **data, const struct rte_hash_bucket *bkt)  {
>  	int i;
> @@ -1032,30 +1047,30 @@ static inline int32_t
> __rte_hash_lookup_with_hash(const struct rte_hash *h, const void *key,
>  					hash_sig_t sig, void **data)
>  {
> -	uint32_t bucket_idx;
> -	hash_sig_t alt_hash;
> +	uint32_t prim_bucket_idx, sec_bucket_idx;
>  	struct rte_hash_bucket *bkt, *cur_bkt;
>  	int ret;
> +	uint16_t short_sig;
> 
> -	bucket_idx = sig & h->bucket_bitmask;
> -	bkt = &h->buckets[bucket_idx];
> +	short_sig = get_short_sig(sig);
> +	prim_bucket_idx = get_prim_bucket_index(h, sig);
> +	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
> +	bkt = &h->buckets[prim_bucket_idx];
> 
>  	__hash_rw_reader_lock(h);
> 
>  	/* Check if key is in primary location */
> -	ret = search_one_bucket(h, key, sig, data, bkt);
> +	ret = search_one_bucket(h, key, short_sig, data, bkt);
>  	if (ret != -1) {
>  		__hash_rw_reader_unlock(h);
>  		return ret;
>  	}
>  	/* Calculate secondary hash */
> -	alt_hash = rte_hash_secondary_hash(sig);
> -	bucket_idx = alt_hash & h->bucket_bitmask;
> -	bkt = &h->buckets[bucket_idx];
> +	bkt = &h->buckets[sec_bucket_idx];
> 
>  	/* Check if key is in secondary location */
>  	FOR_EACH_BUCKET(cur_bkt, bkt) {
> -		ret = search_one_bucket(h, key, alt_hash, data, cur_bkt);
> +		ret = search_one_bucket(h, key, short_sig, data, cur_bkt);
>  		if (ret != -1) {
>  			__hash_rw_reader_unlock(h);
>  			return ret;
> @@ -1102,7 +1117,6 @@ remove_entry(const struct rte_hash *h, struct
> rte_hash_bucket *bkt, unsigned i)
>  	struct lcore_cache *cached_free_slots;
> 
>  	bkt->sig_current[i] = NULL_SIGNATURE;
> -	bkt->sig_alt[i] = NULL_SIGNATURE;
>  	if (h->multi_writer_support) {
>  		lcore_id = rte_lcore_id();
>  		cached_free_slots = &h->local_free_slots[lcore_id]; @@ -
> 1141,9 +1155,7 @@ __rte_hash_compact_ll(struct rte_hash_bucket *cur_bkt,
> int pos) {
>  		if (last_bkt->key_idx[i] != EMPTY_SLOT) {
>  			cur_bkt->key_idx[pos] = last_bkt->key_idx[i];
>  			cur_bkt->sig_current[pos] = last_bkt->sig_current[i];
> -			cur_bkt->sig_alt[pos] = last_bkt->sig_alt[i];
>  			last_bkt->sig_current[i] = NULL_SIGNATURE;
> -			last_bkt->sig_alt[i] = NULL_SIGNATURE;
>  			last_bkt->key_idx[i] = EMPTY_SLOT;
>  			return;
>  		}
> @@ -1153,7 +1165,7 @@ __rte_hash_compact_ll(struct rte_hash_bucket
> *cur_bkt, int pos) {
>  /* Search one bucket and remove the matched key */  static inline int32_t
> search_and_remove(const struct rte_hash *h, const void *key,
> -			struct rte_hash_bucket *bkt, hash_sig_t sig, int *pos)
> +			struct rte_hash_bucket *bkt, uint16_t sig, int *pos)
>  {
>  	struct rte_hash_key *k, *keys = h->key_store;
>  	unsigned int i;
> @@ -1185,19 +1197,21 @@ static inline int32_t
> __rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
>  						hash_sig_t sig)
>  {
> -	uint32_t bucket_idx;
> -	hash_sig_t alt_hash;
> +	uint32_t prim_bucket_idx, sec_bucket_idx;
>  	struct rte_hash_bucket *prim_bkt, *sec_bkt, *prev_bkt, *last_bkt;
>  	struct rte_hash_bucket *cur_bkt;
>  	int pos;
>  	int32_t ret, i;
> +	uint16_t short_sig;
> 
> -	bucket_idx = sig & h->bucket_bitmask;
> -	prim_bkt = &h->buckets[bucket_idx];
> +	short_sig = get_short_sig(sig);
> +	prim_bucket_idx = get_prim_bucket_index(h, sig);
> +	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
> +	prim_bkt = &h->buckets[prim_bucket_idx];
> 
>  	__hash_rw_writer_lock(h);
>  	/* look for key in primary bucket */
> -	ret = search_and_remove(h, key, prim_bkt, sig, &pos);
> +	ret = search_and_remove(h, key, prim_bkt, short_sig, &pos);
>  	if (ret != -1) {
>  		__rte_hash_compact_ll(prim_bkt, pos);
>  		last_bkt = prim_bkt->next;
> @@ -1206,12 +1220,10 @@ __rte_hash_del_key_with_hash(const struct
> rte_hash *h, const void *key,
>  	}
> 
>  	/* Calculate secondary hash */
> -	alt_hash = rte_hash_secondary_hash(sig);
> -	bucket_idx = alt_hash & h->bucket_bitmask;
> -	sec_bkt = &h->buckets[bucket_idx];
> +	sec_bkt = &h->buckets[sec_bucket_idx];
> 
>  	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
> -		ret = search_and_remove(h, key, cur_bkt, alt_hash, &pos);
> +		ret = search_and_remove(h, key, cur_bkt, short_sig, &pos);
>  		if (ret != -1) {
>  			__rte_hash_compact_ll(cur_bkt, pos);
>  			last_bkt = sec_bkt->next;
> @@ -1288,55 +1300,35 @@ static inline void  compare_signatures(uint32_t
> *prim_hash_matches, uint32_t *sec_hash_matches,
>  			const struct rte_hash_bucket *prim_bkt,
>  			const struct rte_hash_bucket *sec_bkt,
> -			hash_sig_t prim_hash, hash_sig_t sec_hash,
> +			uint16_t sig,
>  			enum rte_hash_sig_compare_function sig_cmp_fn)  {
>  	unsigned int i;
> 
> +	/* For match mask the first bit of every two bits indicates the match
> +*/
>  	switch (sig_cmp_fn) {
> -#ifdef RTE_MACHINE_CPUFLAG_AVX2
> -	case RTE_HASH_COMPARE_AVX2:
> -		*prim_hash_matches =
> _mm256_movemask_ps((__m256)_mm256_cmpeq_epi32(
> -				_mm256_load_si256(
> -					(__m256i const *)prim_bkt-
> >sig_current),
> -				_mm256_set1_epi32(prim_hash)));
> -		*sec_hash_matches =
> _mm256_movemask_ps((__m256)_mm256_cmpeq_epi32(
> -				_mm256_load_si256(
> -					(__m256i const *)sec_bkt-
> >sig_current),
> -				_mm256_set1_epi32(sec_hash)));
> -		break;
> -#endif
>  #ifdef RTE_MACHINE_CPUFLAG_SSE2
>  	case RTE_HASH_COMPARE_SSE:
> -		/* Compare the first 4 signatures in the bucket */
> -		*prim_hash_matches =
> _mm_movemask_ps((__m128)_mm_cmpeq_epi16(
> +		/* Compare all signatures in the bucket */
> +		*prim_hash_matches =
> _mm_movemask_epi8(_mm_cmpeq_epi16(
>  				_mm_load_si128(
>  					(__m128i const *)prim_bkt-
> >sig_current),
> -				_mm_set1_epi32(prim_hash)));
> -		*prim_hash_matches |=
> (_mm_movemask_ps((__m128)_mm_cmpeq_epi16(
> -				_mm_load_si128(
> -					(__m128i const *)&prim_bkt-
> >sig_current[4]),
> -				_mm_set1_epi32(prim_hash)))) << 4;
> -		/* Compare the first 4 signatures in the bucket */
> -		*sec_hash_matches =
> _mm_movemask_ps((__m128)_mm_cmpeq_epi16(
> +				_mm_set1_epi16(sig)));
> +		/* Compare all signatures in the bucket */
> +		*sec_hash_matches =
> _mm_movemask_epi8(_mm_cmpeq_epi16(
>  				_mm_load_si128(
>  					(__m128i const *)sec_bkt-
> >sig_current),
> -				_mm_set1_epi32(sec_hash)));
> -		*sec_hash_matches |=
> (_mm_movemask_ps((__m128)_mm_cmpeq_epi16(
> -				_mm_load_si128(
> -					(__m128i const *)&sec_bkt-
> >sig_current[4]),
> -				_mm_set1_epi32(sec_hash)))) << 4;
> +				_mm_set1_epi16(sig)));
>  		break;
>  #endif
>  	default:
>  		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
>  			*prim_hash_matches |=
> -				((prim_hash == prim_bkt->sig_current[i]) << i);
> +				((sig == prim_bkt->sig_current[i]) << (i << 1));
>  			*sec_hash_matches |=
> -				((sec_hash == sec_bkt->sig_current[i]) << i);
> +				((sig == sec_bkt->sig_current[i]) << (i << 1));
>  		}
>  	}
> -
>  }
> 
>  #define PREFETCH_OFFSET 4
> @@ -1349,7 +1341,9 @@ __rte_hash_lookup_bulk(const struct rte_hash *h,
> const void **keys,
>  	int32_t i;
>  	int32_t ret;
>  	uint32_t prim_hash[RTE_HASH_LOOKUP_BULK_MAX];
> -	uint32_t sec_hash[RTE_HASH_LOOKUP_BULK_MAX];
> +	uint32_t prim_index[RTE_HASH_LOOKUP_BULK_MAX];
> +	uint32_t sec_index[RTE_HASH_LOOKUP_BULK_MAX];
> +	uint16_t sig[RTE_HASH_LOOKUP_BULK_MAX];
>  	const struct rte_hash_bucket
> *primary_bkt[RTE_HASH_LOOKUP_BULK_MAX];
>  	const struct rte_hash_bucket
> *secondary_bkt[RTE_HASH_LOOKUP_BULK_MAX];
>  	uint32_t prim_hitmask[RTE_HASH_LOOKUP_BULK_MAX] = {0}; @@ -
> 1368,10 +1362,13 @@ __rte_hash_lookup_bulk(const struct rte_hash *h,
> const void **keys,
>  		rte_prefetch0(keys[i + PREFETCH_OFFSET]);
> 
>  		prim_hash[i] = rte_hash_hash(h, keys[i]);
> -		sec_hash[i] = rte_hash_secondary_hash(prim_hash[i]);
> 
> -		primary_bkt[i] = &h->buckets[prim_hash[i] & h-
> >bucket_bitmask];
> -		secondary_bkt[i] = &h->buckets[sec_hash[i] & h-
> >bucket_bitmask];
> +		sig[i] = get_short_sig(prim_hash[i]);
> +		prim_index[i] = get_prim_bucket_index(h, prim_hash[i]);
> +		sec_index[i] = get_alt_bucket_index(h, prim_index[i], sig[i]);
> +
> +		primary_bkt[i] = &h->buckets[prim_index[i]];
> +		secondary_bkt[i] = &h->buckets[sec_index[i]];
> 
>  		rte_prefetch0(primary_bkt[i]);
>  		rte_prefetch0(secondary_bkt[i]);
> @@ -1380,10 +1377,13 @@ __rte_hash_lookup_bulk(const struct rte_hash
> *h, const void **keys,
>  	/* Calculate and prefetch rest of the buckets */
>  	for (; i < num_keys; i++) {
>  		prim_hash[i] = rte_hash_hash(h, keys[i]);
> -		sec_hash[i] = rte_hash_secondary_hash(prim_hash[i]);
> 
> -		primary_bkt[i] = &h->buckets[prim_hash[i] & h-
> >bucket_bitmask];
> -		secondary_bkt[i] = &h->buckets[sec_hash[i] & h-
> >bucket_bitmask];
> +		sig[i] = get_short_sig(prim_hash[i]);
> +		prim_index[i] = get_prim_bucket_index(h, prim_hash[i]);
> +		sec_index[i] = get_alt_bucket_index(h, prim_index[i], sig[i]);
> +
> +		primary_bkt[i] = &h->buckets[prim_index[i]];
> +		secondary_bkt[i] = &h->buckets[sec_index[i]];
> 
>  		rte_prefetch0(primary_bkt[i]);
>  		rte_prefetch0(secondary_bkt[i]);
> @@ -1394,10 +1394,11 @@ __rte_hash_lookup_bulk(const struct rte_hash
> *h, const void **keys,
>  	for (i = 0; i < num_keys; i++) {
>  		compare_signatures(&prim_hitmask[i], &sec_hitmask[i],
>  				primary_bkt[i], secondary_bkt[i],
> -				prim_hash[i], sec_hash[i], h->sig_cmp_fn);
> +				sig[i], h->sig_cmp_fn);
> 
>  		if (prim_hitmask[i]) {
> -			uint32_t first_hit = __builtin_ctzl(prim_hitmask[i]);
> +			uint32_t first_hit =
> +					__builtin_ctzl(prim_hitmask[i]) >> 1;
>  			uint32_t key_idx = primary_bkt[i]->key_idx[first_hit];
>  			const struct rte_hash_key *key_slot =
>  				(const struct rte_hash_key *)(
> @@ -1408,7 +1409,8 @@ __rte_hash_lookup_bulk(const struct rte_hash *h,
> const void **keys,
>  		}
> 
>  		if (sec_hitmask[i]) {
> -			uint32_t first_hit = __builtin_ctzl(sec_hitmask[i]);
> +			uint32_t first_hit =
> +					__builtin_ctzl(sec_hitmask[i]) >> 1;
>  			uint32_t key_idx = secondary_bkt[i]-
> >key_idx[first_hit];
>  			const struct rte_hash_key *key_slot =
>  				(const struct rte_hash_key *)(
> @@ -1422,7 +1424,8 @@ __rte_hash_lookup_bulk(const struct rte_hash *h,
> const void **keys,
>  	for (i = 0; i < num_keys; i++) {
>  		positions[i] = -ENOENT;
>  		while (prim_hitmask[i]) {
> -			uint32_t hit_index = __builtin_ctzl(prim_hitmask[i]);
> +			uint32_t hit_index =
> +					__builtin_ctzl(prim_hitmask[i]) >> 1;
> 
>  			uint32_t key_idx = primary_bkt[i]->key_idx[hit_index];
>  			const struct rte_hash_key *key_slot = @@ -1441,11
> +1444,12 @@ __rte_hash_lookup_bulk(const struct rte_hash *h, const void
> **keys,
>  				positions[i] = key_idx - 1;
>  				goto next_key;
>  			}
> -			prim_hitmask[i] &= ~(1 << (hit_index));
> +			prim_hitmask[i] &= ~(3ULL << (hit_index << 1));
>  		}
> 
>  		while (sec_hitmask[i]) {
> -			uint32_t hit_index = __builtin_ctzl(sec_hitmask[i]);
> +			uint32_t hit_index =
> +					__builtin_ctzl(sec_hitmask[i]) >> 1;
> 
>  			uint32_t key_idx = secondary_bkt[i]-
> >key_idx[hit_index];
>  			const struct rte_hash_key *key_slot = @@ -1465,7
> +1469,7 @@ __rte_hash_lookup_bulk(const struct rte_hash *h, const void
> **keys,
>  				positions[i] = key_idx - 1;
>  				goto next_key;
>  			}
> -			sec_hitmask[i] &= ~(1 << (hit_index));
> +			sec_hitmask[i] &= ~(3ULL << (hit_index << 1));
>  		}
> 
>  next_key:
> @@ -1488,10 +1492,10 @@ __rte_hash_lookup_bulk(const struct rte_hash
> *h, const void **keys,
>  		FOR_EACH_BUCKET(cur_bkt, next_bkt) {
>  			if (data != NULL)
>  				ret = search_one_bucket(h, keys[i],
> -						sec_hash[i], &data[i],
> cur_bkt);
> +						sig[i], &data[i], cur_bkt);
>  			else
>  				ret = search_one_bucket(h, keys[i],
> -						sec_hash[i], NULL, cur_bkt);
> +						sig[i], NULL, cur_bkt);
>  			if (ret != -1) {
>  				positions[i] = ret;
>  				hits |= 1ULL << i;
> diff --git a/lib/librte_hash/rte_cuckoo_hash.h
> b/lib/librte_hash/rte_cuckoo_hash.h
> index e601520..7753cd8 100644
> --- a/lib/librte_hash/rte_cuckoo_hash.h
> +++ b/lib/librte_hash/rte_cuckoo_hash.h
> @@ -129,18 +129,15 @@ struct rte_hash_key {  enum
> rte_hash_sig_compare_function {
>  	RTE_HASH_COMPARE_SCALAR = 0,
>  	RTE_HASH_COMPARE_SSE,
> -	RTE_HASH_COMPARE_AVX2,
>  	RTE_HASH_COMPARE_NUM
>  };
> 
>  /** Bucket structure */
>  struct rte_hash_bucket {
> -	hash_sig_t sig_current[RTE_HASH_BUCKET_ENTRIES];
> +	uint16_t sig_current[RTE_HASH_BUCKET_ENTRIES];
> 
>  	uint32_t key_idx[RTE_HASH_BUCKET_ENTRIES];
> 
> -	hash_sig_t sig_alt[RTE_HASH_BUCKET_ENTRIES];
> -
>  	uint8_t flag[RTE_HASH_BUCKET_ENTRIES];
> 
>  	void *next;
> @@ -193,6 +190,7 @@ struct rte_hash {
> 
>  struct queue_node {
>  	struct rte_hash_bucket *bkt; /* Current bucket on the bfs search */
> +	uint32_t cur_bkt_idx;
> 
>  	struct queue_node *prev;     /* Parent(bucket) in search path */
>  	int prev_slot;               /* Parent(slot) in search path */
> diff --git a/lib/librte_hash/rte_hash.h b/lib/librte_hash/rte_hash.h index
> 11d8e28..6ace64e 100644
> --- a/lib/librte_hash/rte_hash.h
> +++ b/lib/librte_hash/rte_hash.h
> @@ -40,7 +40,10 @@ extern "C" {
>  /** Flag to indicate the extendabe bucket table feature should be used */
> #define RTE_HASH_EXTRA_FLAGS_EXT_TABLE 0x08
> 
> -/** Signature of key that is stored internally. */
> +/**
> + * The type of hash value of a key.
> + * It should be a value of at least 32bit with fully random pattern.
> + */
>  typedef uint32_t hash_sig_t;
> 
>  /** Type of function that can be used for calculating the hash value. */
> --
> 2.7.4
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
diff mbox series

Patch

diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index 02650b9..e101708 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -90,6 +90,36 @@  rte_hash_cmp_eq(const void *key1, const void *key2, const struct rte_hash *h)
 		return cmp_jump_table[h->cmp_jump_table_idx](key1, key2, h->key_len);
 }
 
+/*
+ * We use higher 16 bits of hash as the signature value stored in table.
+ * We use the lower bits for the primary bucket
+ * location. Then we XOR primary bucket location and the signature
+ * to get the secondary bucket location. This is same as
+ * proposed in Bin Fan, et al's paper
+ * "MemC3: Compact and Concurrent MemCache with Dumber Caching and
+ * Smarter Hashing". The benefit to use
+ * XOR is that one could derive the alternative bucket location
+ * by only using the current bucket location and the signature.
+ */
+static inline uint16_t
+get_short_sig(const hash_sig_t hash)
+{
+	return hash >> 16;
+}
+
+static inline uint32_t
+get_prim_bucket_index(const struct rte_hash *h, const hash_sig_t hash)
+{
+	return hash & h->bucket_bitmask;
+}
+
+static inline uint32_t
+get_alt_bucket_index(const struct rte_hash *h,
+			uint32_t cur_bkt_idx, uint16_t sig)
+{
+	return (cur_bkt_idx ^ sig) & h->bucket_bitmask;
+}
+
 struct rte_hash *
 rte_hash_create(const struct rte_hash_parameters *params)
 {
@@ -327,9 +357,7 @@  rte_hash_create(const struct rte_hash_parameters *params)
 	h->ext_table_support = ext_table_support;
 
 #if defined(RTE_ARCH_X86)
-	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX2))
-		h->sig_cmp_fn = RTE_HASH_COMPARE_AVX2;
-	else if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE2))
+	if (rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE2))
 		h->sig_cmp_fn = RTE_HASH_COMPARE_SSE;
 	else
 #endif
@@ -417,18 +445,6 @@  rte_hash_hash(const struct rte_hash *h, const void *key)
 	return h->hash_func(key, h->key_len, h->hash_func_init_val);
 }
 
-/* Calc the secondary hash value from the primary hash value of a given key */
-static inline hash_sig_t
-rte_hash_secondary_hash(const hash_sig_t primary_hash)
-{
-	static const unsigned all_bits_shift = 12;
-	static const unsigned alt_bits_xor = 0x5bd1e995;
-
-	uint32_t tag = primary_hash >> all_bits_shift;
-
-	return primary_hash ^ ((tag + 1) * alt_bits_xor);
-}
-
 int32_t
 rte_hash_count(const struct rte_hash *h)
 {
@@ -560,14 +576,13 @@  enqueue_slot_back(const struct rte_hash *h,
 /* Search a key from bucket and update its data */
 static inline int32_t
 search_and_update(const struct rte_hash *h, void *data, const void *key,
-	struct rte_hash_bucket *bkt, hash_sig_t sig, hash_sig_t alt_hash)
+	struct rte_hash_bucket *bkt, uint16_t sig)
 {
 	int i;
 	struct rte_hash_key *k, *keys = h->key_store;
 
 	for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
-		if (bkt->sig_current[i] == sig &&
-				bkt->sig_alt[i] == alt_hash) {
+		if (bkt->sig_current[i] == sig) {
 			k = (struct rte_hash_key *) ((char *)keys +
 					bkt->key_idx[i] * h->key_entry_size);
 			if (rte_hash_cmp_eq(key, k->key, h) == 0) {
@@ -594,7 +609,7 @@  rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
 		struct rte_hash_bucket *prim_bkt,
 		struct rte_hash_bucket *sec_bkt,
 		const struct rte_hash_key *key, void *data,
-		hash_sig_t sig, hash_sig_t alt_hash, uint32_t new_idx,
+		uint16_t sig, uint32_t new_idx,
 		int32_t *ret_val)
 {
 	unsigned int i;
@@ -605,7 +620,7 @@  rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
 	/* Check if key was inserted after last check but before this
 	 * protected region in case of inserting duplicated keys.
 	 */
-	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
+	ret = search_and_update(h, data, key, prim_bkt, sig);
 	if (ret != -1) {
 		__hash_rw_writer_unlock(h);
 		*ret_val = ret;
@@ -613,7 +628,7 @@  rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
 	}
 
 	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
-		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
+		ret = search_and_update(h, data, key, cur_bkt, sig);
 		if (ret != -1) {
 			__hash_rw_writer_unlock(h);
 			*ret_val = ret;
@@ -628,7 +643,6 @@  rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
 		/* Check if slot is available */
 		if (likely(prim_bkt->key_idx[i] == EMPTY_SLOT)) {
 			prim_bkt->sig_current[i] = sig;
-			prim_bkt->sig_alt[i] = alt_hash;
 			prim_bkt->key_idx[i] = new_idx;
 			break;
 		}
@@ -653,7 +667,7 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 			struct rte_hash_bucket *alt_bkt,
 			const struct rte_hash_key *key, void *data,
 			struct queue_node *leaf, uint32_t leaf_slot,
-			hash_sig_t sig, hash_sig_t alt_hash, uint32_t new_idx,
+			uint16_t sig, uint32_t new_idx,
 			int32_t *ret_val)
 {
 	uint32_t prev_alt_bkt_idx;
@@ -674,7 +688,7 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 	/* Check if key was inserted after last check but before this
 	 * protected region.
 	 */
-	ret = search_and_update(h, data, key, bkt, sig, alt_hash);
+	ret = search_and_update(h, data, key, bkt, sig);
 	if (ret != -1) {
 		__hash_rw_writer_unlock(h);
 		*ret_val = ret;
@@ -682,7 +696,7 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 	}
 
 	FOR_EACH_BUCKET(cur_bkt, alt_bkt) {
-		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
+		ret = search_and_update(h, data, key, cur_bkt, sig);
 		if (ret != -1) {
 			__hash_rw_writer_unlock(h);
 			*ret_val = ret;
@@ -695,8 +709,9 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 		prev_bkt = prev_node->bkt;
 		prev_slot = curr_node->prev_slot;
 
-		prev_alt_bkt_idx =
-			prev_bkt->sig_alt[prev_slot] & h->bucket_bitmask;
+		prev_alt_bkt_idx = get_alt_bucket_index(h,
+					prev_node->cur_bkt_idx,
+					prev_bkt->sig_current[prev_slot]);
 
 		if (unlikely(&h->buckets[prev_alt_bkt_idx]
 				!= curr_bkt)) {
@@ -710,10 +725,8 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 		 * Cuckoo insert to move elements back to its
 		 * primary bucket if available
 		 */
-		curr_bkt->sig_alt[curr_slot] =
-			 prev_bkt->sig_current[prev_slot];
 		curr_bkt->sig_current[curr_slot] =
-			prev_bkt->sig_alt[prev_slot];
+			prev_bkt->sig_current[prev_slot];
 		curr_bkt->key_idx[curr_slot] =
 			prev_bkt->key_idx[prev_slot];
 
@@ -723,7 +736,6 @@  rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
 	}
 
 	curr_bkt->sig_current[curr_slot] = sig;
-	curr_bkt->sig_alt[curr_slot] = alt_hash;
 	curr_bkt->key_idx[curr_slot] = new_idx;
 
 	__hash_rw_writer_unlock(h);
@@ -741,39 +753,44 @@  rte_hash_cuckoo_make_space_mw(const struct rte_hash *h,
 			struct rte_hash_bucket *bkt,
 			struct rte_hash_bucket *sec_bkt,
 			const struct rte_hash_key *key, void *data,
-			hash_sig_t sig, hash_sig_t alt_hash,
+			uint16_t sig, uint32_t bucket_idx,
 			uint32_t new_idx, int32_t *ret_val)
 {
 	unsigned int i;
 	struct queue_node queue[RTE_HASH_BFS_QUEUE_MAX_LEN];
 	struct queue_node *tail, *head;
 	struct rte_hash_bucket *curr_bkt, *alt_bkt;
+	uint32_t cur_idx, alt_idx;
 
 	tail = queue;
 	head = queue + 1;
 	tail->bkt = bkt;
 	tail->prev = NULL;
 	tail->prev_slot = -1;
+	tail->cur_bkt_idx = bucket_idx;
 
 	/* Cuckoo bfs Search */
 	while (likely(tail != head && head <
 					queue + RTE_HASH_BFS_QUEUE_MAX_LEN -
 					RTE_HASH_BUCKET_ENTRIES)) {
 		curr_bkt = tail->bkt;
+		cur_idx = tail->cur_bkt_idx;
 		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
 			if (curr_bkt->key_idx[i] == EMPTY_SLOT) {
 				int32_t ret = rte_hash_cuckoo_move_insert_mw(h,
 						bkt, sec_bkt, key, data,
-						tail, i, sig, alt_hash,
+						tail, i, sig,
 						new_idx, ret_val);
 				if (likely(ret != -1))
 					return ret;
 			}
 
 			/* Enqueue new node and keep prev node info */
-			alt_bkt = &(h->buckets[curr_bkt->sig_alt[i]
-						    & h->bucket_bitmask]);
+			alt_idx = get_alt_bucket_index(h, cur_idx,
+						curr_bkt->sig_current[i]);
+			alt_bkt = &(h->buckets[alt_idx]);
 			head->bkt = alt_bkt;
+			head->cur_bkt_idx = alt_idx;
 			head->prev = tail;
 			head->prev_slot = i;
 			head++;
@@ -788,7 +805,7 @@  static inline int32_t
 __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 						hash_sig_t sig, void *data)
 {
-	hash_sig_t alt_hash;
+	uint16_t short_sig;
 	uint32_t prim_bucket_idx, sec_bucket_idx;
 	struct rte_hash_bucket *prim_bkt, *sec_bkt, *cur_bkt;
 	struct rte_hash_key *new_k, *keys = h->key_store;
@@ -803,18 +820,17 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 	int32_t ret_val;
 	struct rte_hash_bucket *last;
 
-	prim_bucket_idx = sig & h->bucket_bitmask;
+	short_sig = get_short_sig(sig);
+	prim_bucket_idx = get_prim_bucket_index(h, sig);
+	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
 	prim_bkt = &h->buckets[prim_bucket_idx];
-	rte_prefetch0(prim_bkt);
-
-	alt_hash = rte_hash_secondary_hash(sig);
-	sec_bucket_idx = alt_hash & h->bucket_bitmask;
 	sec_bkt = &h->buckets[sec_bucket_idx];
+	rte_prefetch0(prim_bkt);
 	rte_prefetch0(sec_bkt);
 
 	/* Check if key is already inserted in primary location */
 	__hash_rw_writer_lock(h);
-	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
+	ret = search_and_update(h, data, key, prim_bkt, short_sig);
 	if (ret != -1) {
 		__hash_rw_writer_unlock(h);
 		return ret;
@@ -822,12 +838,13 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 
 	/* Check if key is already inserted in secondary location */
 	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
-		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
+		ret = search_and_update(h, data, key, cur_bkt, short_sig);
 		if (ret != -1) {
 			__hash_rw_writer_unlock(h);
 			return ret;
 		}
 	}
+
 	__hash_rw_writer_unlock(h);
 
 	/* Did not find a match, so get a new slot for storing the new key */
@@ -865,7 +882,7 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 
 	/* Find an empty slot and insert */
 	ret = rte_hash_cuckoo_insert_mw(h, prim_bkt, sec_bkt, key, data,
-					sig, alt_hash, new_idx, &ret_val);
+					short_sig, new_idx, &ret_val);
 	if (ret == 0)
 		return new_idx - 1;
 	else if (ret == 1) {
@@ -875,7 +892,7 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 
 	/* Primary bucket full, need to make space for new entry */
 	ret = rte_hash_cuckoo_make_space_mw(h, prim_bkt, sec_bkt, key, data,
-					sig, alt_hash, new_idx, &ret_val);
+				short_sig, prim_bucket_idx, new_idx, &ret_val);
 	if (ret == 0)
 		return new_idx - 1;
 	else if (ret == 1) {
@@ -885,7 +902,7 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 
 	/* Also search secondary bucket to get better occupancy */
 	ret = rte_hash_cuckoo_make_space_mw(h, sec_bkt, prim_bkt, key, data,
-					alt_hash, sig, new_idx, &ret_val);
+				short_sig, sec_bucket_idx, new_idx, &ret_val);
 
 	if (ret == 0)
 		return new_idx - 1;
@@ -905,14 +922,14 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 	 */
 	__hash_rw_writer_lock(h);
 	/* We check for duplicates again since could be inserted before the lock */
-	ret = search_and_update(h, data, key, prim_bkt, sig, alt_hash);
+	ret = search_and_update(h, data, key, prim_bkt, short_sig);
 	if (ret != -1) {
 		enqueue_slot_back(h, cached_free_slots, slot_id);
 		goto failure;
 	}
 
 	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
-		ret = search_and_update(h, data, key, cur_bkt, alt_hash, sig);
+		ret = search_and_update(h, data, key, cur_bkt, short_sig);
 		if (ret != -1) {
 			enqueue_slot_back(h, cached_free_slots, slot_id);
 			goto failure;
@@ -924,8 +941,7 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
 			/* Check if slot is available */
 			if (likely(cur_bkt->key_idx[i] == EMPTY_SLOT)) {
-				cur_bkt->sig_current[i] = alt_hash;
-				cur_bkt->sig_alt[i] = sig;
+				cur_bkt->sig_current[i] = short_sig;
 				cur_bkt->key_idx[i] = new_idx;
 				__hash_rw_writer_unlock(h);
 				return new_idx - 1;
@@ -943,8 +959,7 @@  __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
 
 	bkt_id = (uint32_t)((uintptr_t)ext_bkt_id) - 1;
 	/* Use the first location of the new bucket */
-	(h->buckets_ext[bkt_id]).sig_current[0] = alt_hash;
-	(h->buckets_ext[bkt_id]).sig_alt[0] = sig;
+	(h->buckets_ext[bkt_id]).sig_current[0] = short_sig;
 	(h->buckets_ext[bkt_id]).key_idx[0] = new_idx;
 	/* Link the new bucket to sec bucket linked list */
 	last = rte_hash_get_last_bkt(sec_bkt);
@@ -1003,7 +1018,7 @@  rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data)
 
 /* Search one bucket to find the match key */
 static inline int32_t
-search_one_bucket(const struct rte_hash *h, const void *key, hash_sig_t sig,
+search_one_bucket(const struct rte_hash *h, const void *key, uint16_t sig,
 			void **data, const struct rte_hash_bucket *bkt)
 {
 	int i;
@@ -1032,30 +1047,30 @@  static inline int32_t
 __rte_hash_lookup_with_hash(const struct rte_hash *h, const void *key,
 					hash_sig_t sig, void **data)
 {
-	uint32_t bucket_idx;
-	hash_sig_t alt_hash;
+	uint32_t prim_bucket_idx, sec_bucket_idx;
 	struct rte_hash_bucket *bkt, *cur_bkt;
 	int ret;
+	uint16_t short_sig;
 
-	bucket_idx = sig & h->bucket_bitmask;
-	bkt = &h->buckets[bucket_idx];
+	short_sig = get_short_sig(sig);
+	prim_bucket_idx = get_prim_bucket_index(h, sig);
+	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
+	bkt = &h->buckets[prim_bucket_idx];
 
 	__hash_rw_reader_lock(h);
 
 	/* Check if key is in primary location */
-	ret = search_one_bucket(h, key, sig, data, bkt);
+	ret = search_one_bucket(h, key, short_sig, data, bkt);
 	if (ret != -1) {
 		__hash_rw_reader_unlock(h);
 		return ret;
 	}
 	/* Calculate secondary hash */
-	alt_hash = rte_hash_secondary_hash(sig);
-	bucket_idx = alt_hash & h->bucket_bitmask;
-	bkt = &h->buckets[bucket_idx];
+	bkt = &h->buckets[sec_bucket_idx];
 
 	/* Check if key is in secondary location */
 	FOR_EACH_BUCKET(cur_bkt, bkt) {
-		ret = search_one_bucket(h, key, alt_hash, data, cur_bkt);
+		ret = search_one_bucket(h, key, short_sig, data, cur_bkt);
 		if (ret != -1) {
 			__hash_rw_reader_unlock(h);
 			return ret;
@@ -1102,7 +1117,6 @@  remove_entry(const struct rte_hash *h, struct rte_hash_bucket *bkt, unsigned i)
 	struct lcore_cache *cached_free_slots;
 
 	bkt->sig_current[i] = NULL_SIGNATURE;
-	bkt->sig_alt[i] = NULL_SIGNATURE;
 	if (h->multi_writer_support) {
 		lcore_id = rte_lcore_id();
 		cached_free_slots = &h->local_free_slots[lcore_id];
@@ -1141,9 +1155,7 @@  __rte_hash_compact_ll(struct rte_hash_bucket *cur_bkt, int pos) {
 		if (last_bkt->key_idx[i] != EMPTY_SLOT) {
 			cur_bkt->key_idx[pos] = last_bkt->key_idx[i];
 			cur_bkt->sig_current[pos] = last_bkt->sig_current[i];
-			cur_bkt->sig_alt[pos] = last_bkt->sig_alt[i];
 			last_bkt->sig_current[i] = NULL_SIGNATURE;
-			last_bkt->sig_alt[i] = NULL_SIGNATURE;
 			last_bkt->key_idx[i] = EMPTY_SLOT;
 			return;
 		}
@@ -1153,7 +1165,7 @@  __rte_hash_compact_ll(struct rte_hash_bucket *cur_bkt, int pos) {
 /* Search one bucket and remove the matched key */
 static inline int32_t
 search_and_remove(const struct rte_hash *h, const void *key,
-			struct rte_hash_bucket *bkt, hash_sig_t sig, int *pos)
+			struct rte_hash_bucket *bkt, uint16_t sig, int *pos)
 {
 	struct rte_hash_key *k, *keys = h->key_store;
 	unsigned int i;
@@ -1185,19 +1197,21 @@  static inline int32_t
 __rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
 						hash_sig_t sig)
 {
-	uint32_t bucket_idx;
-	hash_sig_t alt_hash;
+	uint32_t prim_bucket_idx, sec_bucket_idx;
 	struct rte_hash_bucket *prim_bkt, *sec_bkt, *prev_bkt, *last_bkt;
 	struct rte_hash_bucket *cur_bkt;
 	int pos;
 	int32_t ret, i;
+	uint16_t short_sig;
 
-	bucket_idx = sig & h->bucket_bitmask;
-	prim_bkt = &h->buckets[bucket_idx];
+	short_sig = get_short_sig(sig);
+	prim_bucket_idx = get_prim_bucket_index(h, sig);
+	sec_bucket_idx = get_alt_bucket_index(h, prim_bucket_idx, short_sig);
+	prim_bkt = &h->buckets[prim_bucket_idx];
 
 	__hash_rw_writer_lock(h);
 	/* look for key in primary bucket */
-	ret = search_and_remove(h, key, prim_bkt, sig, &pos);
+	ret = search_and_remove(h, key, prim_bkt, short_sig, &pos);
 	if (ret != -1) {
 		__rte_hash_compact_ll(prim_bkt, pos);
 		last_bkt = prim_bkt->next;
@@ -1206,12 +1220,10 @@  __rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
 	}
 
 	/* Calculate secondary hash */
-	alt_hash = rte_hash_secondary_hash(sig);
-	bucket_idx = alt_hash & h->bucket_bitmask;
-	sec_bkt = &h->buckets[bucket_idx];
+	sec_bkt = &h->buckets[sec_bucket_idx];
 
 	FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
-		ret = search_and_remove(h, key, cur_bkt, alt_hash, &pos);
+		ret = search_and_remove(h, key, cur_bkt, short_sig, &pos);
 		if (ret != -1) {
 			__rte_hash_compact_ll(cur_bkt, pos);
 			last_bkt = sec_bkt->next;
@@ -1288,55 +1300,35 @@  static inline void
 compare_signatures(uint32_t *prim_hash_matches, uint32_t *sec_hash_matches,
 			const struct rte_hash_bucket *prim_bkt,
 			const struct rte_hash_bucket *sec_bkt,
-			hash_sig_t prim_hash, hash_sig_t sec_hash,
+			uint16_t sig,
 			enum rte_hash_sig_compare_function sig_cmp_fn)
 {
 	unsigned int i;
 
+	/* For match mask the first bit of every two bits indicates the match */
 	switch (sig_cmp_fn) {
-#ifdef RTE_MACHINE_CPUFLAG_AVX2
-	case RTE_HASH_COMPARE_AVX2:
-		*prim_hash_matches = _mm256_movemask_ps((__m256)_mm256_cmpeq_epi32(
-				_mm256_load_si256(
-					(__m256i const *)prim_bkt->sig_current),
-				_mm256_set1_epi32(prim_hash)));
-		*sec_hash_matches = _mm256_movemask_ps((__m256)_mm256_cmpeq_epi32(
-				_mm256_load_si256(
-					(__m256i const *)sec_bkt->sig_current),
-				_mm256_set1_epi32(sec_hash)));
-		break;
-#endif
 #ifdef RTE_MACHINE_CPUFLAG_SSE2
 	case RTE_HASH_COMPARE_SSE:
-		/* Compare the first 4 signatures in the bucket */
-		*prim_hash_matches = _mm_movemask_ps((__m128)_mm_cmpeq_epi16(
+		/* Compare all signatures in the bucket */
+		*prim_hash_matches = _mm_movemask_epi8(_mm_cmpeq_epi16(
 				_mm_load_si128(
 					(__m128i const *)prim_bkt->sig_current),
-				_mm_set1_epi32(prim_hash)));
-		*prim_hash_matches |= (_mm_movemask_ps((__m128)_mm_cmpeq_epi16(
-				_mm_load_si128(
-					(__m128i const *)&prim_bkt->sig_current[4]),
-				_mm_set1_epi32(prim_hash)))) << 4;
-		/* Compare the first 4 signatures in the bucket */
-		*sec_hash_matches = _mm_movemask_ps((__m128)_mm_cmpeq_epi16(
+				_mm_set1_epi16(sig)));
+		/* Compare all signatures in the bucket */
+		*sec_hash_matches = _mm_movemask_epi8(_mm_cmpeq_epi16(
 				_mm_load_si128(
 					(__m128i const *)sec_bkt->sig_current),
-				_mm_set1_epi32(sec_hash)));
-		*sec_hash_matches |= (_mm_movemask_ps((__m128)_mm_cmpeq_epi16(
-				_mm_load_si128(
-					(__m128i const *)&sec_bkt->sig_current[4]),
-				_mm_set1_epi32(sec_hash)))) << 4;
+				_mm_set1_epi16(sig)));
 		break;
 #endif
 	default:
 		for (i = 0; i < RTE_HASH_BUCKET_ENTRIES; i++) {
 			*prim_hash_matches |=
-				((prim_hash == prim_bkt->sig_current[i]) << i);
+				((sig == prim_bkt->sig_current[i]) << (i << 1));
 			*sec_hash_matches |=
-				((sec_hash == sec_bkt->sig_current[i]) << i);
+				((sig == sec_bkt->sig_current[i]) << (i << 1));
 		}
 	}
-
 }
 
 #define PREFETCH_OFFSET 4
@@ -1349,7 +1341,9 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 	int32_t i;
 	int32_t ret;
 	uint32_t prim_hash[RTE_HASH_LOOKUP_BULK_MAX];
-	uint32_t sec_hash[RTE_HASH_LOOKUP_BULK_MAX];
+	uint32_t prim_index[RTE_HASH_LOOKUP_BULK_MAX];
+	uint32_t sec_index[RTE_HASH_LOOKUP_BULK_MAX];
+	uint16_t sig[RTE_HASH_LOOKUP_BULK_MAX];
 	const struct rte_hash_bucket *primary_bkt[RTE_HASH_LOOKUP_BULK_MAX];
 	const struct rte_hash_bucket *secondary_bkt[RTE_HASH_LOOKUP_BULK_MAX];
 	uint32_t prim_hitmask[RTE_HASH_LOOKUP_BULK_MAX] = {0};
@@ -1368,10 +1362,13 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 		rte_prefetch0(keys[i + PREFETCH_OFFSET]);
 
 		prim_hash[i] = rte_hash_hash(h, keys[i]);
-		sec_hash[i] = rte_hash_secondary_hash(prim_hash[i]);
 
-		primary_bkt[i] = &h->buckets[prim_hash[i] & h->bucket_bitmask];
-		secondary_bkt[i] = &h->buckets[sec_hash[i] & h->bucket_bitmask];
+		sig[i] = get_short_sig(prim_hash[i]);
+		prim_index[i] = get_prim_bucket_index(h, prim_hash[i]);
+		sec_index[i] = get_alt_bucket_index(h, prim_index[i], sig[i]);
+
+		primary_bkt[i] = &h->buckets[prim_index[i]];
+		secondary_bkt[i] = &h->buckets[sec_index[i]];
 
 		rte_prefetch0(primary_bkt[i]);
 		rte_prefetch0(secondary_bkt[i]);
@@ -1380,10 +1377,13 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 	/* Calculate and prefetch rest of the buckets */
 	for (; i < num_keys; i++) {
 		prim_hash[i] = rte_hash_hash(h, keys[i]);
-		sec_hash[i] = rte_hash_secondary_hash(prim_hash[i]);
 
-		primary_bkt[i] = &h->buckets[prim_hash[i] & h->bucket_bitmask];
-		secondary_bkt[i] = &h->buckets[sec_hash[i] & h->bucket_bitmask];
+		sig[i] = get_short_sig(prim_hash[i]);
+		prim_index[i] = get_prim_bucket_index(h, prim_hash[i]);
+		sec_index[i] = get_alt_bucket_index(h, prim_index[i], sig[i]);
+
+		primary_bkt[i] = &h->buckets[prim_index[i]];
+		secondary_bkt[i] = &h->buckets[sec_index[i]];
 
 		rte_prefetch0(primary_bkt[i]);
 		rte_prefetch0(secondary_bkt[i]);
@@ -1394,10 +1394,11 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 	for (i = 0; i < num_keys; i++) {
 		compare_signatures(&prim_hitmask[i], &sec_hitmask[i],
 				primary_bkt[i], secondary_bkt[i],
-				prim_hash[i], sec_hash[i], h->sig_cmp_fn);
+				sig[i], h->sig_cmp_fn);
 
 		if (prim_hitmask[i]) {
-			uint32_t first_hit = __builtin_ctzl(prim_hitmask[i]);
+			uint32_t first_hit =
+					__builtin_ctzl(prim_hitmask[i]) >> 1;
 			uint32_t key_idx = primary_bkt[i]->key_idx[first_hit];
 			const struct rte_hash_key *key_slot =
 				(const struct rte_hash_key *)(
@@ -1408,7 +1409,8 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 		}
 
 		if (sec_hitmask[i]) {
-			uint32_t first_hit = __builtin_ctzl(sec_hitmask[i]);
+			uint32_t first_hit =
+					__builtin_ctzl(sec_hitmask[i]) >> 1;
 			uint32_t key_idx = secondary_bkt[i]->key_idx[first_hit];
 			const struct rte_hash_key *key_slot =
 				(const struct rte_hash_key *)(
@@ -1422,7 +1424,8 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 	for (i = 0; i < num_keys; i++) {
 		positions[i] = -ENOENT;
 		while (prim_hitmask[i]) {
-			uint32_t hit_index = __builtin_ctzl(prim_hitmask[i]);
+			uint32_t hit_index =
+					__builtin_ctzl(prim_hitmask[i]) >> 1;
 
 			uint32_t key_idx = primary_bkt[i]->key_idx[hit_index];
 			const struct rte_hash_key *key_slot =
@@ -1441,11 +1444,12 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 				positions[i] = key_idx - 1;
 				goto next_key;
 			}
-			prim_hitmask[i] &= ~(1 << (hit_index));
+			prim_hitmask[i] &= ~(3ULL << (hit_index << 1));
 		}
 
 		while (sec_hitmask[i]) {
-			uint32_t hit_index = __builtin_ctzl(sec_hitmask[i]);
+			uint32_t hit_index =
+					__builtin_ctzl(sec_hitmask[i]) >> 1;
 
 			uint32_t key_idx = secondary_bkt[i]->key_idx[hit_index];
 			const struct rte_hash_key *key_slot =
@@ -1465,7 +1469,7 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 				positions[i] = key_idx - 1;
 				goto next_key;
 			}
-			sec_hitmask[i] &= ~(1 << (hit_index));
+			sec_hitmask[i] &= ~(3ULL << (hit_index << 1));
 		}
 
 next_key:
@@ -1488,10 +1492,10 @@  __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
 		FOR_EACH_BUCKET(cur_bkt, next_bkt) {
 			if (data != NULL)
 				ret = search_one_bucket(h, keys[i],
-						sec_hash[i], &data[i], cur_bkt);
+						sig[i], &data[i], cur_bkt);
 			else
 				ret = search_one_bucket(h, keys[i],
-						sec_hash[i], NULL, cur_bkt);
+						sig[i], NULL, cur_bkt);
 			if (ret != -1) {
 				positions[i] = ret;
 				hits |= 1ULL << i;
diff --git a/lib/librte_hash/rte_cuckoo_hash.h b/lib/librte_hash/rte_cuckoo_hash.h
index e601520..7753cd8 100644
--- a/lib/librte_hash/rte_cuckoo_hash.h
+++ b/lib/librte_hash/rte_cuckoo_hash.h
@@ -129,18 +129,15 @@  struct rte_hash_key {
 enum rte_hash_sig_compare_function {
 	RTE_HASH_COMPARE_SCALAR = 0,
 	RTE_HASH_COMPARE_SSE,
-	RTE_HASH_COMPARE_AVX2,
 	RTE_HASH_COMPARE_NUM
 };
 
 /** Bucket structure */
 struct rte_hash_bucket {
-	hash_sig_t sig_current[RTE_HASH_BUCKET_ENTRIES];
+	uint16_t sig_current[RTE_HASH_BUCKET_ENTRIES];
 
 	uint32_t key_idx[RTE_HASH_BUCKET_ENTRIES];
 
-	hash_sig_t sig_alt[RTE_HASH_BUCKET_ENTRIES];
-
 	uint8_t flag[RTE_HASH_BUCKET_ENTRIES];
 
 	void *next;
@@ -193,6 +190,7 @@  struct rte_hash {
 
 struct queue_node {
 	struct rte_hash_bucket *bkt; /* Current bucket on the bfs search */
+	uint32_t cur_bkt_idx;
 
 	struct queue_node *prev;     /* Parent(bucket) in search path */
 	int prev_slot;               /* Parent(slot) in search path */
diff --git a/lib/librte_hash/rte_hash.h b/lib/librte_hash/rte_hash.h
index 11d8e28..6ace64e 100644
--- a/lib/librte_hash/rte_hash.h
+++ b/lib/librte_hash/rte_hash.h
@@ -40,7 +40,10 @@  extern "C" {
 /** Flag to indicate the extendabe bucket table feature should be used */
 #define RTE_HASH_EXTRA_FLAGS_EXT_TABLE 0x08
 
-/** Signature of key that is stored internally. */
+/**
+ * The type of hash value of a key.
+ * It should be a value of at least 32bit with fully random pattern.
+ */
 typedef uint32_t hash_sig_t;
 
 /** Type of function that can be used for calculating the hash value. */