hash: support lock-free extendable bucket
authorDharmik Thakkar <dharmik.thakkar@arm.com>
Tue, 2 Apr 2019 19:44:54 +0000 (19:44 +0000)
committerThomas Monjalon <thomas@monjalon.net>
Wed, 3 Apr 2019 18:52:35 +0000 (20:52 +0200)
This patch enables lock-free read-write concurrency support for
extendable bucket feature.

Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Yipeng Wang <yipeng1.wang@intel.com>
doc/guides/prog_guide/hash_lib.rst
lib/librte_hash/rte_cuckoo_hash.c
lib/librte_hash/rte_cuckoo_hash.h

index 85a6edf..d06c7de 100644 (file)
@@ -108,9 +108,9 @@ Extendable Bucket Functionality support
 An extra flag is used to enable this functionality (flag is not set by default). When the (RTE_HASH_EXTRA_FLAGS_EXT_TABLE) is set and
 in the very unlikely case due to excessive hash collisions that a key has failed to be inserted, the hash table bucket is extended with a linked
 list to insert these failed keys. This feature is important for the workloads (e.g. telco workloads) that need to insert up to 100% of the
-hash table size and can't tolerate any key insertion failure (even if very few). Currently the extendable bucket is not supported
-with the lock-free concurrency implementation (RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF).
-
+hash table size and can't tolerate any key insertion failure (even if very few).
+Please note that with the 'lock free read/write concurrency' flag enabled, users need to call 'rte_hash_free_key_with_position' API in order to free the empty buckets and
+deleted keys, to maintain the 100% capacity guarantee.
 
 Implementation Details (non Extendable Bucket Case)
 ---------------------------------------------------
index 0dddce2..4fcf548 100644 (file)
@@ -141,6 +141,7 @@ rte_hash_create(const struct rte_hash_parameters *params)
        unsigned int readwrite_concur_support = 0;
        unsigned int writer_takes_lock = 0;
        unsigned int no_free_on_del = 0;
+       uint32_t *ext_bkt_to_free = NULL;
        uint32_t *tbl_chng_cnt = NULL;
        unsigned int readwrite_concur_lf_support = 0;
 
@@ -171,15 +172,6 @@ rte_hash_create(const struct rte_hash_parameters *params)
                return NULL;
        }
 
-       if ((params->extra_flag & RTE_HASH_EXTRA_FLAGS_RW_CONCURRENCY_LF) &&
-           (params->extra_flag & RTE_HASH_EXTRA_FLAGS_EXT_TABLE)) {
-               rte_errno = EINVAL;
-               RTE_LOG(ERR, HASH, "rte_hash_create: extendable bucket "
-                       "feature not supported with rw concurrency "
-                       "lock free\n");
-               return NULL;
-       }
-
        /* Check extra flags field to check extra options. */
        if (params->extra_flag & RTE_HASH_EXTRA_FLAGS_TRANS_MEM_SUPPORT)
                hw_trans_mem_support = 1;
@@ -303,6 +295,16 @@ rte_hash_create(const struct rte_hash_parameters *params)
                 */
                for (i = 1; i <= num_buckets; i++)
                        rte_ring_sp_enqueue(r_ext, (void *)((uintptr_t) i));
+
+               if (readwrite_concur_lf_support) {
+                       ext_bkt_to_free = rte_zmalloc(NULL, sizeof(uint32_t) *
+                                                               num_key_slots, 0);
+                       if (ext_bkt_to_free == NULL) {
+                               RTE_LOG(ERR, HASH, "ext bkt to free memory allocation "
+                                                               "failed\n");
+                               goto err_unlock;
+                       }
+               }
        }
 
        const uint32_t key_entry_size =
@@ -394,6 +396,7 @@ rte_hash_create(const struct rte_hash_parameters *params)
                default_hash_func : params->hash_func;
        h->key_store = k;
        h->free_slots = r;
+       h->ext_bkt_to_free = ext_bkt_to_free;
        h->tbl_chng_cnt = tbl_chng_cnt;
        *h->tbl_chng_cnt = 0;
        h->hw_trans_mem_support = hw_trans_mem_support;
@@ -448,6 +451,7 @@ err:
        rte_free(buckets_ext);
        rte_free(k);
        rte_free(tbl_chng_cnt);
+       rte_free(ext_bkt_to_free);
        return NULL;
 }
 
@@ -489,6 +493,7 @@ rte_hash_free(struct rte_hash *h)
        rte_free(h->buckets);
        rte_free(h->buckets_ext);
        rte_free(h->tbl_chng_cnt);
+       rte_free(h->ext_bkt_to_free);
        rte_free(h);
        rte_free(te);
 }
@@ -804,7 +809,7 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
                        __atomic_store_n(h->tbl_chng_cnt,
                                         *h->tbl_chng_cnt + 1,
                                         __ATOMIC_RELEASE);
-                       /* The stores to sig_alt and sig_current should not
+                       /* The store to sig_current should not
                         * move above the store to tbl_chng_cnt.
                         */
                        __atomic_thread_fence(__ATOMIC_RELEASE);
@@ -836,7 +841,7 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
                __atomic_store_n(h->tbl_chng_cnt,
                                 *h->tbl_chng_cnt + 1,
                                 __ATOMIC_RELEASE);
-               /* The stores to sig_alt and sig_current should not
+               /* The store to sig_current should not
                 * move above the store to tbl_chng_cnt.
                 */
                __atomic_thread_fence(__ATOMIC_RELEASE);
@@ -1059,7 +1064,12 @@ __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
                        /* Check if slot is available */
                        if (likely(cur_bkt->key_idx[i] == EMPTY_SLOT)) {
                                cur_bkt->sig_current[i] = short_sig;
-                               cur_bkt->key_idx[i] = new_idx;
+                               /* Store to signature should not leak after
+                                * the store to key_idx
+                                */
+                               __atomic_store_n(&cur_bkt->key_idx[i],
+                                                new_idx,
+                                                __ATOMIC_RELEASE);
                                __hash_rw_writer_unlock(h);
                                return new_idx - 1;
                        }
@@ -1077,7 +1087,12 @@ __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] = short_sig;
-       (h->buckets_ext[bkt_id]).key_idx[0] = new_idx;
+       /* Store to signature should not leak after
+        * the store to key_idx
+        */
+       __atomic_store_n(&(h->buckets_ext[bkt_id]).key_idx[0],
+                        new_idx,
+                        __ATOMIC_RELEASE);
        /* Link the new bucket to sec bucket linked list */
        last = rte_hash_get_last_bkt(sec_bkt);
        last->next = &h->buckets_ext[bkt_id];
@@ -1371,7 +1386,8 @@ remove_entry(const struct rte_hash *h, struct rte_hash_bucket *bkt, unsigned i)
  * empty slot.
  */
 static inline void
-__rte_hash_compact_ll(struct rte_hash_bucket *cur_bkt, int pos) {
+__rte_hash_compact_ll(const struct rte_hash *h,
+                       struct rte_hash_bucket *cur_bkt, int pos) {
        int i;
        struct rte_hash_bucket *last_bkt;
 
@@ -1382,10 +1398,27 @@ __rte_hash_compact_ll(struct rte_hash_bucket *cur_bkt, int pos) {
 
        for (i = RTE_HASH_BUCKET_ENTRIES - 1; i >= 0; i--) {
                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];
+                       __atomic_store_n(&cur_bkt->key_idx[pos],
+                                        last_bkt->key_idx[i],
+                                        __ATOMIC_RELEASE);
+                       if (h->readwrite_concur_lf_support) {
+                               /* Inform the readers that the table has changed
+                                * Since there is one writer, load acquire on
+                                * tbl_chng_cnt is not required.
+                                */
+                               __atomic_store_n(h->tbl_chng_cnt,
+                                        *h->tbl_chng_cnt + 1,
+                                        __ATOMIC_RELEASE);
+                               /* The store to sig_current should
+                                * not move above the store to tbl_chng_cnt.
+                                */
+                               __atomic_thread_fence(__ATOMIC_RELEASE);
+                       }
                        last_bkt->sig_current[i] = NULL_SIGNATURE;
-                       last_bkt->key_idx[i] = EMPTY_SLOT;
+                       __atomic_store_n(&last_bkt->key_idx[i],
+                                        EMPTY_SLOT,
+                                        __ATOMIC_RELEASE);
                        return;
                }
        }
@@ -1454,7 +1487,7 @@ __rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
        /* look for key in primary bucket */
        ret = search_and_remove(h, key, prim_bkt, short_sig, &pos);
        if (ret != -1) {
-               __rte_hash_compact_ll(prim_bkt, pos);
+               __rte_hash_compact_ll(h, prim_bkt, pos);
                last_bkt = prim_bkt->next;
                prev_bkt = prim_bkt;
                goto return_bkt;
@@ -1466,7 +1499,7 @@ __rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key,
        FOR_EACH_BUCKET(cur_bkt, sec_bkt) {
                ret = search_and_remove(h, key, cur_bkt, short_sig, &pos);
                if (ret != -1) {
-                       __rte_hash_compact_ll(cur_bkt, pos);
+                       __rte_hash_compact_ll(h, cur_bkt, pos);
                        last_bkt = sec_bkt->next;
                        prev_bkt = sec_bkt;
                        goto return_bkt;
@@ -1493,11 +1526,24 @@ return_bkt:
        }
        /* found empty bucket and recycle */
        if (i == RTE_HASH_BUCKET_ENTRIES) {
-               prev_bkt->next = last_bkt->next = NULL;
+               prev_bkt->next = NULL;
                uint32_t index = last_bkt - h->buckets_ext + 1;
-               rte_ring_sp_enqueue(h->free_ext_bkts, (void *)(uintptr_t)index);
+               /* Recycle the empty bkt if
+                * no_free_on_del is disabled.
+                */
+               if (h->no_free_on_del)
+                       /* Store index of an empty ext bkt to be recycled
+                        * on calling rte_hash_del_xxx APIs.
+                        * When lock free read-write concurrency is enabled,
+                        * an empty ext bkt cannot be put into free list
+                        * immediately (as readers might be using it still).
+                        * Hence freeing of the ext bkt is piggy-backed to
+                        * freeing of the key index.
+                        */
+                       h->ext_bkt_to_free[ret] = index;
+               else
+                       rte_ring_sp_enqueue(h->free_ext_bkts, (void *)(uintptr_t)index);
        }
-
        __hash_rw_writer_unlock(h);
        return ret;
 }
@@ -1550,6 +1596,14 @@ rte_hash_free_key_with_position(const struct rte_hash *h,
        /* Out of bounds */
        if (position >= total_entries)
                return -EINVAL;
+       if (h->ext_table_support && h->readwrite_concur_lf_support) {
+               uint32_t index = h->ext_bkt_to_free[position];
+               if (index) {
+                       /* Recycle empty ext bkt to free list. */
+                       rte_ring_sp_enqueue(h->free_ext_bkts, (void *)(uintptr_t)index);
+                       h->ext_bkt_to_free[position] = 0;
+               }
+       }
 
        if (h->use_local_cache) {
                lcore_id = rte_lcore_id();
@@ -1882,6 +1936,9 @@ __rte_hash_lookup_bulk_lf(const struct rte_hash *h, const void **keys,
                rte_prefetch0(secondary_bkt[i]);
        }
 
+       for (i = 0; i < num_keys; i++)
+               positions[i] = -ENOENT;
+
        do {
                /* Load the table change counter before the lookup
                 * starts. Acquire semantics will make sure that
@@ -1926,7 +1983,6 @@ __rte_hash_lookup_bulk_lf(const struct rte_hash *h, const void **keys,
 
                /* Compare keys, first hits in primary first */
                for (i = 0; i < num_keys; i++) {
-                       positions[i] = -ENOENT;
                        while (prim_hitmask[i]) {
                                uint32_t hit_index =
                                                __builtin_ctzl(prim_hitmask[i])
@@ -1999,6 +2055,35 @@ next_key:
                        continue;
                }
 
+               /* all found, do not need to go through ext bkt */
+               if (hits == ((1ULL << num_keys) - 1)) {
+                       if (hit_mask != NULL)
+                               *hit_mask = hits;
+                       return;
+               }
+               /* need to check ext buckets for match */
+               if (h->ext_table_support) {
+                       for (i = 0; i < num_keys; i++) {
+                               if ((hits & (1ULL << i)) != 0)
+                                       continue;
+                               next_bkt = secondary_bkt[i]->next;
+                               FOR_EACH_BUCKET(cur_bkt, next_bkt) {
+                                       if (data != NULL)
+                                               ret = search_one_bucket_lf(h,
+                                                       keys[i], sig[i],
+                                                       &data[i], cur_bkt);
+                                       else
+                                               ret = search_one_bucket_lf(h,
+                                                               keys[i], sig[i],
+                                                               NULL, cur_bkt);
+                                       if (ret != -1) {
+                                               positions[i] = ret;
+                                               hits |= 1ULL << i;
+                                               break;
+                                       }
+                               }
+                       }
+               }
                /* The loads of sig_current in compare_signatures
                 * should not move below the load from tbl_chng_cnt.
                 */
@@ -2015,34 +2100,6 @@ next_key:
                                        __ATOMIC_ACQUIRE);
        } while (cnt_b != cnt_a);
 
-       /* all found, do not need to go through ext bkt */
-       if ((hits == ((1ULL << num_keys) - 1)) || !h->ext_table_support) {
-               if (hit_mask != NULL)
-                       *hit_mask = hits;
-               __hash_rw_reader_unlock(h);
-               return;
-       }
-
-       /* need to check ext buckets for match */
-       for (i = 0; i < num_keys; i++) {
-               if ((hits & (1ULL << i)) != 0)
-                       continue;
-               next_bkt = secondary_bkt[i]->next;
-               FOR_EACH_BUCKET(cur_bkt, next_bkt) {
-                       if (data != NULL)
-                               ret = search_one_bucket_lf(h, keys[i],
-                                               sig[i], &data[i], cur_bkt);
-                       else
-                               ret = search_one_bucket_lf(h, keys[i],
-                                               sig[i], NULL, cur_bkt);
-                       if (ret != -1) {
-                               positions[i] = ret;
-                               hits |= 1ULL << i;
-                               break;
-                       }
-               }
-       }
-
        if (hit_mask != NULL)
                *hit_mask = hits;
 }
index 0548c97..fb19bb2 100644 (file)
@@ -211,6 +211,13 @@ struct rte_hash {
        rte_rwlock_t *readwrite_lock; /**< Read-write lock thread-safety. */
        struct rte_hash_bucket *buckets_ext; /**< Extra buckets array */
        struct rte_ring *free_ext_bkts; /**< Ring of indexes of free buckets */
+       /* Stores index of an empty ext bkt to be recycled on calling
+        * rte_hash_del_xxx APIs. When lock free read-write concurrency is
+        * enabled, an empty ext bkt cannot be put into free list immediately
+        * (as readers might be using it still). Hence freeing of the ext bkt
+        * is piggy-backed to freeing of the key index.
+        */
+       uint32_t *ext_bkt_to_free;
        uint32_t *tbl_chng_cnt;
        /**< Indicates if the hash table changed from last read. */
 } __rte_cache_aligned;