This patch enables lock-free read-write concurrency support for
extendable bucket feature.
Suggested-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
Signed-off-by: Dharmik Thakkar <dharmik.thak...@arm.com>
---
doc/guides/prog_guide/hash_lib.rst | 3 +-
lib/librte_hash/rte_cuckoo_hash.c | 150 +++++++++++++++++++----------
lib/librte_hash/rte_cuckoo_hash.h | 8 ++
3 files changed, 110 insertions(+), 51 deletions(-)
diff --git a/doc/guides/prog_guide/hash_lib.rst
b/doc/guides/prog_guide/hash_lib.rst
index 85a6edfa8b16..b00446e949ba 100644
--- a/doc/guides/prog_guide/hash_lib.rst
+++ b/doc/guides/prog_guide/hash_lib.rst
@@ -108,8 +108,7 @@ 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).
Implementation Details (non Extendable Bucket Case)
diff --git a/lib/librte_hash/rte_cuckoo_hash.c
b/lib/librte_hash/rte_cuckoo_hash.c
index c01489ba5193..54762533ce36 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -170,15 +170,6 @@ 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;
@@ -1054,7 +1045,15 @@ __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;
+ /* Key can be of arbitrary length, so it is
+ * not possible to store it atomically.
+ * Hence the new key element's memory stores
+ * (key as well as data) should be complete
+ * before it is referenced.
+ */
+ __atomic_store_n(&cur_bkt->key_idx[i],
+ new_idx,
+ __ATOMIC_RELEASE);
__hash_rw_writer_unlock(h);
return new_idx - 1;
}
@@ -1072,10 +1071,23 @@ __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;
+ /* Key can be of arbitrary length, so it is
+ * not possible to store it atomically.
+ * Hence the new key element's memory stores
+ * (key as well as data) should be complete
+ * before it is referenced.
+ */
+ __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];
+ /* New bucket's memory stores (key as well as data)
+ * should be complete before it is referenced
+ */
+ __atomic_store_n(&last->next,
+ &h->buckets_ext[bkt_id],
+ __ATOMIC_RELEASE);
__hash_rw_writer_unlock(h);
return new_idx - 1;
@@ -1366,7 +1378,8 @@ 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;
@@ -1377,10 +1390,27 @@ __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 acquires on
+ * tbl_chng_cnt are not required.
+ */
+ __atomic_store_n(h->tbl_chng_cnt,
+ *h->tbl_chng_cnt + 1,
+ __ATOMIC_RELEASE);
+ /* The stores to sig_alt and 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;
}
}
@@ -1449,7 +1479,7 @@ __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;
@@ -1461,7 +1491,7 @@ __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;
@@ -1488,11 +1518,21 @@ __rte_hash_del_key_with_hash(const struct rte_hash *h,
const void *key,
}
/* found empty bucket and recycle */
if (i == RTE_HASH_BUCKET_ENTRIES) {
- prev_bkt->next = last_bkt->next = NULL;
+ __atomic_store_n(&prev_bkt->next,
+ NULL,
+ __ATOMIC_RELEASE);
uint32_t index = last_bkt - h->buckets_ext + 1;
- rte_ring_sp_enqueue(h->free_ext_bkts, (void *)(uintptr_t)index);
- }
+ if (!h->no_free_on_del)
+ rte_ring_sp_enqueue(h->free_ext_bkts, (void
*)(uintptr_t)index);
+ else {
+ struct rte_hash_key *key_slot =
+ (struct rte_hash_key *)(
+ (char *)h->key_store +
+ ret * h->key_entry_size);
+ key_slot->ext_bkt_to_free = index;
+ }
+ }
__hash_rw_writer_unlock(h);
return ret;
}
@@ -1567,6 +1607,14 @@ rte_hash_free_key_with_position(const struct rte_hash *h,
(void *)((uintptr_t)position));
}
+ const struct rte_hash_key *key_slot = (const struct rte_hash_key *)(
+ (const char *)h->key_store +
+ position * h->key_entry_size);
+ uint32_t index = key_slot->ext_bkt_to_free;
+ if (!index)
+ /* Recycle empty ext bkt to free list. */
+ rte_ring_sp_enqueue(h->free_ext_bkts, (void *)(uintptr_t)index);
+
return 0;
}
@@ -1855,6 +1903,9 @@ __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
@@ -1899,7 +1950,6 @@ __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])
@@ -1972,6 +2022,36 @@ __rte_hash_lookup_bulk_lf(const struct rte_hash *h,
const void **keys,
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.
*/
@@ -1988,34 +2068,6 @@ __rte_hash_lookup_bulk_lf(const struct rte_hash *h,
const void **keys,
__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;
}
diff --git a/lib/librte_hash/rte_cuckoo_hash.h
b/lib/librte_hash/rte_cuckoo_hash.h
index eacdaa8d4684..062cc2dd0296 100644
--- a/lib/librte_hash/rte_cuckoo_hash.h
+++ b/lib/librte_hash/rte_cuckoo_hash.h
@@ -129,6 +129,14 @@ struct lcore_cache {
/* Structure that stores key-value pair */
struct rte_hash_key {
+ /* Stores index of an empty ext bkt to be recycled on calling
+ * rte_hash_del_xxx APIs. When lock free read-wrie 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;
+
union {
uintptr_t idata;
void *pdata;
--
2.17.1
