[dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys
Honnappa Nagarahalli
honnappa.nagarahalli at arm.com
Thu Sep 6 19:12:17 CEST 2018
Reader-writer concurrency issue, caused by moving the keys
to their alternative locations during key insert, is solved
by introducing a global counter(tbl_chng_cnt) indicating a
change in table.
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Reviewed-by: Gavin Hu <gavin.hu at arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
Reviewed-by: Steve Capper <steve.capper at arm.com>
---
lib/librte_hash/rte_cuckoo_hash.c | 307 +++++++++++++++++++++++++-------------
lib/librte_hash/rte_cuckoo_hash.h | 2 +
lib/librte_hash/rte_hash.h | 8 +-
3 files changed, 206 insertions(+), 111 deletions(-)
diff --git a/lib/librte_hash/rte_cuckoo_hash.c b/lib/librte_hash/rte_cuckoo_hash.c
index 2d89158..1e4a8d4 100644
--- a/lib/librte_hash/rte_cuckoo_hash.c
+++ b/lib/librte_hash/rte_cuckoo_hash.c
@@ -256,6 +256,7 @@ rte_hash_create(const struct rte_hash_parameters *params)
#endif
/* Setup hash context */
snprintf(h->name, sizeof(h->name), "%s", params->name);
+ h->tbl_chng_cnt = 0;
h->entries = params->entries;
h->key_len = params->key_len;
h->key_entry_size = key_entry_size;
@@ -588,7 +589,7 @@ rte_hash_cuckoo_insert_mw(const struct rte_hash *h,
* return 0 if succeeds.
*/
static inline int
-rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
+rte_hash_cuckoo_move_insert_mw(struct rte_hash *h,
struct rte_hash_bucket *bkt,
struct rte_hash_bucket *alt_bkt,
const struct rte_hash_key *key, void *data,
@@ -639,11 +640,27 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
if (unlikely(&h->buckets[prev_alt_bkt_idx]
!= curr_bkt)) {
/* revert it to empty, otherwise duplicated keys */
- curr_bkt->key_idx[curr_slot] = EMPTY_SLOT;
+ __atomic_store_n(&curr_bkt->key_idx[curr_slot],
+ EMPTY_SLOT,
+ __ATOMIC_RELEASE);
__hash_rw_writer_unlock(h);
return -1;
}
+ /* Inform the previous move. The current move need
+ * not be informed now as the current bucket entry
+ * is present in both primary and secondary.
+ * 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);
+
/* Need to swap current/alt sig to allow later
* Cuckoo insert to move elements back to its
* primary bucket if available
@@ -662,6 +679,20 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
curr_bkt = curr_node->bkt;
}
+ /* Inform the previous move. The current move need
+ * not be informed now as the current bucket entry
+ * is present in both primary and secondary.
+ * 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);
+
curr_bkt->sig_current[curr_slot] = sig;
curr_bkt->sig_alt[curr_slot] = alt_hash;
/* Release the new bucket entry */
@@ -680,7 +711,7 @@ rte_hash_cuckoo_move_insert_mw(const struct rte_hash *h,
* Cuckoo
*/
static inline int
-rte_hash_cuckoo_make_space_mw(const struct rte_hash *h,
+rte_hash_cuckoo_make_space_mw(struct rte_hash *h,
struct rte_hash_bucket *bkt,
struct rte_hash_bucket *sec_bkt,
const struct rte_hash_key *key, void *data,
@@ -728,7 +759,7 @@ rte_hash_cuckoo_make_space_mw(const struct rte_hash *h,
}
static inline int32_t
-__rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
+__rte_hash_add_key_with_hash(struct rte_hash *h, const void *key,
hash_sig_t sig, void *data)
{
hash_sig_t alt_hash;
@@ -844,7 +875,7 @@ __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
}
int32_t
-rte_hash_add_key_with_hash(const struct rte_hash *h,
+rte_hash_add_key_with_hash(struct rte_hash *h,
const void *key, hash_sig_t sig)
{
RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
@@ -852,14 +883,14 @@ rte_hash_add_key_with_hash(const struct rte_hash *h,
}
int32_t
-rte_hash_add_key(const struct rte_hash *h, const void *key)
+rte_hash_add_key(struct rte_hash *h, const void *key)
{
RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
return __rte_hash_add_key_with_hash(h, key, rte_hash_hash(h, key), 0);
}
int
-rte_hash_add_key_with_hash_data(const struct rte_hash *h,
+rte_hash_add_key_with_hash_data(struct rte_hash *h,
const void *key, hash_sig_t sig, void *data)
{
int ret;
@@ -873,7 +904,7 @@ rte_hash_add_key_with_hash_data(const struct rte_hash *h,
}
int
-rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data)
+rte_hash_add_key_data(struct rte_hash *h, const void *key, void *data)
{
int ret;
@@ -926,30 +957,56 @@ __rte_hash_lookup_with_hash(const struct rte_hash *h, const void *key,
uint32_t bucket_idx;
hash_sig_t alt_hash;
struct rte_hash_bucket *bkt;
+ uint32_t cnt_b, cnt_a;
int ret;
- bucket_idx = sig & h->bucket_bitmask;
- bkt = &h->buckets[bucket_idx];
-
__hash_rw_reader_lock(h);
- /* Check if key is in primary location */
- ret = search_one_bucket(h, key, 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];
+ do {
+ /* Load the table change counter before the lookup
+ * starts. Acquire semantics will make sure that
+ * loads in search_one_bucket are not hoisted.
+ */
+ cnt_b = __atomic_load_n(&h->tbl_chng_cnt,
+ __ATOMIC_ACQUIRE);
+
+ bucket_idx = sig & h->bucket_bitmask;
+ bkt = &h->buckets[bucket_idx];
+
+ /* Check if key is in primary location */
+ ret = search_one_bucket(h, key, 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];
+
+ /* Check if key is in secondary location */
+ ret = search_one_bucket(h, key, alt_hash, data, bkt);
+ if (ret != -1) {
+ __hash_rw_reader_unlock(h);
+ return ret;
+ }
+
+ /* The loads of sig_current in search_one_bucket
+ * should not move below the load from tbl_chng_cnt.
+ */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+ /* Re-read the table change counter to check if the
+ * table has changed during search. If yes, re-do
+ * the search.
+ * This load should not get hoisted. The load
+ * acquires on cnt_b, key index in primary bucket
+ * and key index in secondary bucket will make sure
+ * that it does not get hoisted.
+ */
+ cnt_a = __atomic_load_n(&h->tbl_chng_cnt,
+ __ATOMIC_ACQUIRE);
+ } while (cnt_b != cnt_a);
- /* Check if key is in secondary location */
- ret = search_one_bucket(h, key, alt_hash, data, bkt);
- if (ret != -1) {
- __hash_rw_reader_unlock(h);
- return ret;
- }
__hash_rw_reader_unlock(h);
return -ENOENT;
}
@@ -1190,6 +1247,7 @@ __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
uint32_t prim_hitmask[RTE_HASH_LOOKUP_BULK_MAX] = {0};
uint32_t sec_hitmask[RTE_HASH_LOOKUP_BULK_MAX] = {0};
void *pdata[RTE_HASH_LOOKUP_BULK_MAX];
+ uint32_t cnt_b, cnt_a;
/* Prefetch first keys */
for (i = 0; i < PREFETCH_OFFSET && i < num_keys; i++)
@@ -1225,102 +1283,137 @@ __rte_hash_lookup_bulk(const struct rte_hash *h, const void **keys,
}
__hash_rw_reader_lock(h);
- /* Compare signatures and prefetch key slot of first hit */
- for (i = 0; i < num_keys; i++) {
- compare_signatures(&prim_hitmask[i], &sec_hitmask[i],
+ do {
+ /* Load the table change counter before the lookup
+ * starts. Acquire semantics will make sure that
+ * loads in compare_signatures are not hoisted.
+ */
+ cnt_b = __atomic_load_n(&h->tbl_chng_cnt,
+ __ATOMIC_ACQUIRE);
+
+ /* Compare signatures and prefetch key slot of first hit */
+ 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);
- if (prim_hitmask[i]) {
- uint32_t first_hit = __builtin_ctzl(prim_hitmask[i]);
- uint32_t key_idx = primary_bkt[i]->key_idx[first_hit];
- const struct rte_hash_key *key_slot =
- (const struct rte_hash_key *)(
- (const char *)h->key_store +
- key_idx * h->key_entry_size);
- rte_prefetch0(key_slot);
- continue;
- }
+ if (prim_hitmask[i]) {
+ uint32_t first_hit =
+ __builtin_ctzl(prim_hitmask[i]);
+ uint32_t key_idx =
+ primary_bkt[i]->key_idx[first_hit];
+ const struct rte_hash_key *key_slot =
+ (const struct rte_hash_key *)(
+ (const char *)h->key_store +
+ key_idx * h->key_entry_size);
+ rte_prefetch0(key_slot);
+ continue;
+ }
- if (sec_hitmask[i]) {
- uint32_t first_hit = __builtin_ctzl(sec_hitmask[i]);
- uint32_t key_idx = secondary_bkt[i]->key_idx[first_hit];
- const struct rte_hash_key *key_slot =
- (const struct rte_hash_key *)(
- (const char *)h->key_store +
- key_idx * h->key_entry_size);
- rte_prefetch0(key_slot);
+ if (sec_hitmask[i]) {
+ uint32_t first_hit =
+ __builtin_ctzl(sec_hitmask[i]);
+ uint32_t key_idx =
+ secondary_bkt[i]->key_idx[first_hit];
+ const struct rte_hash_key *key_slot =
+ (const struct rte_hash_key *)(
+ (const char *)h->key_store +
+ key_idx * h->key_entry_size);
+ rte_prefetch0(key_slot);
+ }
}
- }
- /* 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]);
+ /* 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]);
- uint32_t key_idx =
- __atomic_load_n(
- &primary_bkt[i]->key_idx[hit_index],
- __ATOMIC_ACQUIRE);
- const struct rte_hash_key *key_slot =
- (const struct rte_hash_key *)(
- (const char *)h->key_store +
- key_idx * h->key_entry_size);
-
- if (key_idx != EMPTY_SLOT)
- pdata[i] = __atomic_load_n(&key_slot->pdata,
- __ATOMIC_ACQUIRE);
- /*
- * If key index is 0, do not compare key,
- * as it is checking the dummy slot
- */
- if (!!key_idx & !rte_hash_cmp_eq(key_slot->key, keys[i], h)) {
- if (data != NULL)
- data[i] = pdata[i];
+ uint32_t key_idx =
+ __atomic_load_n(
+ &primary_bkt[i]->key_idx[hit_index],
+ __ATOMIC_ACQUIRE);
+ const struct rte_hash_key *key_slot =
+ (const struct rte_hash_key *)(
+ (const char *)h->key_store +
+ key_idx * h->key_entry_size);
- hits |= 1ULL << i;
- positions[i] = key_idx - 1;
- goto next_key;
+ if (key_idx != EMPTY_SLOT)
+ pdata[i] = __atomic_load_n(
+ &key_slot->pdata,
+ __ATOMIC_ACQUIRE);
+ /*
+ * If key index is 0, do not compare key,
+ * as it is checking the dummy slot
+ */
+ if (!!key_idx &
+ !rte_hash_cmp_eq(
+ key_slot->key, keys[i], h)) {
+ if (data != NULL)
+ data[i] = pdata[i];
+
+ hits |= 1ULL << i;
+ positions[i] = key_idx - 1;
+ goto next_key;
+ }
+ prim_hitmask[i] &= ~(1 << (hit_index));
}
- prim_hitmask[i] &= ~(1 << (hit_index));
- }
- while (sec_hitmask[i]) {
- uint32_t hit_index = __builtin_ctzl(sec_hitmask[i]);
+ while (sec_hitmask[i]) {
+ uint32_t hit_index =
+ __builtin_ctzl(sec_hitmask[i]);
- uint32_t key_idx =
- __atomic_load_n(
- &secondary_bkt[i]->key_idx[hit_index],
- __ATOMIC_ACQUIRE);
- const struct rte_hash_key *key_slot =
- (const struct rte_hash_key *)(
- (const char *)h->key_store +
- key_idx * h->key_entry_size);
-
- if (key_idx != EMPTY_SLOT)
- pdata[i] = __atomic_load_n(&key_slot->pdata,
- __ATOMIC_ACQUIRE);
-
- /*
- * If key index is 0, do not compare key,
- * as it is checking the dummy slot
- */
+ uint32_t key_idx =
+ __atomic_load_n(
+ &secondary_bkt[i]->key_idx[hit_index],
+ __ATOMIC_ACQUIRE);
+ const struct rte_hash_key *key_slot =
+ (const struct rte_hash_key *)(
+ (const char *)h->key_store +
+ key_idx * h->key_entry_size);
- if (!!key_idx & !rte_hash_cmp_eq(key_slot->key, keys[i], h)) {
- if (data != NULL)
- data[i] = pdata[i];
+ if (key_idx != EMPTY_SLOT)
+ pdata[i] = __atomic_load_n(
+ &key_slot->pdata,
+ __ATOMIC_ACQUIRE);
+ /*
+ * If key index is 0, do not compare key,
+ * as it is checking the dummy slot
+ */
- hits |= 1ULL << i;
- positions[i] = key_idx - 1;
- goto next_key;
+ if (!!key_idx &
+ !rte_hash_cmp_eq(
+ key_slot->key, keys[i], h)) {
+ if (data != NULL)
+ data[i] = pdata[i];
+
+ hits |= 1ULL << i;
+ positions[i] = key_idx - 1;
+ goto next_key;
+ }
+ sec_hitmask[i] &= ~(1 << (hit_index));
}
- sec_hitmask[i] &= ~(1 << (hit_index));
- }
next_key:
- continue;
- }
+ continue;
+ }
+
+ /* The loads of sig_current in compare_signatures
+ * should not move below the load from tbl_chng_cnt.
+ */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+ /* Re-read the table change counter to check if the
+ * table has changed during search. If yes, re-do
+ * the search.
+ * This load should not get hoisted. The load
+ * acquires on cnt_b, primary key index and secondary
+ * key index will make sure that it does not get
+ * hoisted.
+ */
+ cnt_a = __atomic_load_n(&h->tbl_chng_cnt,
+ __ATOMIC_ACQUIRE);
+ } while (cnt_b != cnt_a);
__hash_rw_reader_unlock(h);
diff --git a/lib/librte_hash/rte_cuckoo_hash.h b/lib/librte_hash/rte_cuckoo_hash.h
index b0c7ef9..5ce864c 100644
--- a/lib/librte_hash/rte_cuckoo_hash.h
+++ b/lib/librte_hash/rte_cuckoo_hash.h
@@ -186,6 +186,8 @@ struct rte_hash {
* to the key table.
*/
rte_rwlock_t *readwrite_lock; /**< Read-write lock thread-safety. */
+ uint32_t tbl_chng_cnt;
+ /**< Indicates if the hash table changed from last read. */
} __rte_cache_aligned;
struct queue_node {
diff --git a/lib/librte_hash/rte_hash.h b/lib/librte_hash/rte_hash.h
index 9e7d931..05e024b 100644
--- a/lib/librte_hash/rte_hash.h
+++ b/lib/librte_hash/rte_hash.h
@@ -156,7 +156,7 @@ rte_hash_count(const struct rte_hash *h);
* - -ENOSPC if there is no space in the hash for this key.
*/
int
-rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data);
+rte_hash_add_key_data(struct rte_hash *h, const void *key, void *data);
/**
* Add a key-value pair with a pre-computed hash value
@@ -180,7 +180,7 @@ rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data);
* - -ENOSPC if there is no space in the hash for this key.
*/
int32_t
-rte_hash_add_key_with_hash_data(const struct rte_hash *h, const void *key,
+rte_hash_add_key_with_hash_data(struct rte_hash *h, const void *key,
hash_sig_t sig, void *data);
/**
@@ -200,7 +200,7 @@ rte_hash_add_key_with_hash_data(const struct rte_hash *h, const void *key,
* array of user data. This value is unique for this key.
*/
int32_t
-rte_hash_add_key(const struct rte_hash *h, const void *key);
+rte_hash_add_key(struct rte_hash *h, const void *key);
/**
* Add a key to an existing hash table.
@@ -222,7 +222,7 @@ rte_hash_add_key(const struct rte_hash *h, const void *key);
* array of user data. This value is unique for this key.
*/
int32_t
-rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key, hash_sig_t sig);
+rte_hash_add_key_with_hash(struct rte_hash *h, const void *key, hash_sig_t sig);
/**
* Remove a key from an existing hash table.
--
2.7.4
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