2 * Copyright (c) 2014, 2016 Nicira, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at:
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
26 COVERAGE_DEFINE(cmap_expand);
27 COVERAGE_DEFINE(cmap_shrink);
29 /* Optimistic Concurrent Cuckoo Hash
30 * =================================
32 * A "cuckoo hash" is an open addressing hash table schema, designed such that
33 * a given element can be in one of only a small number of buckets 'd', each of
34 * which holds up to a small number 'k' elements. Thus, the expected and
35 * worst-case lookup times are O(1) because they require comparing no more than
36 * a fixed number of elements (k * d). Inserting a new element can require
37 * moving around existing elements, but it is also O(1) amortized expected
40 * An optimistic concurrent hash table goes one step further, making it
41 * possible for a single writer to execute concurrently with any number of
42 * readers without requiring the readers to take any locks.
44 * This cuckoo hash implementation uses:
46 * - Two hash functions (d=2). More hash functions allow for a higher load
47 * factor, but increasing 'k' is easier and the benefits of increasing 'd'
48 * quickly fall off with the 'k' values used here. Also, the method of
49 * generating hashes used in this implementation is hard to reasonably
50 * extend beyond d=2. Finally, each additional hash function means that a
51 * lookup has to look at least one extra cache line.
53 * - 5 or 7 elements per bucket (k=5 or k=7), chosen to make buckets
54 * exactly one cache line in size.
56 * According to Erlingsson [4], these parameters suggest a maximum load factor
57 * of about 93%. The current implementation is conservative, expanding the
58 * hash table when it is over 85% full.
60 * When the load factor is below 20%, the hash table will be shrinked by half.
61 * This is to reduce the memory utilization of the hash table and to avoid
62 * the hash table occupying the top of heap chunk which prevents the trimming
68 * A cuckoo hash requires multiple hash functions. When reorganizing the hash
69 * becomes too difficult, it also requires the ability to change the hash
70 * functions. Requiring the client to provide multiple hashes and to be able
71 * to change them to new hashes upon insertion is inconvenient.
73 * This implementation takes another approach. The client provides a single,
74 * fixed hash. The cuckoo hash internally "rehashes" this hash against a
75 * randomly selected basis value (see rehash()). This rehashed value is one of
76 * the two hashes. The other hash is computed by 16-bit circular rotation of
77 * the rehashed value. Updating the basis changes the hash functions.
79 * To work properly, the hash functions used by a cuckoo hash must be
80 * independent. If one hash function is a function of the other (e.g. h2(x) =
81 * h1(x) + 1, or h2(x) = hash(h1(x))), then insertion will eventually fail
82 * catastrophically (loop forever) because of collisions. With this rehashing
83 * technique, the two hashes are completely independent for masks up to 16 bits
84 * wide. For masks wider than 16 bits, only 32-n bits are independent between
85 * the two hashes. Thus, it becomes risky to grow a cuckoo hash table beyond
86 * about 2**24 buckets (about 71 million elements with k=5 and maximum load
87 * 85%). Fortunately, Open vSwitch does not normally deal with hash tables
94 * This cuckoo hash table implementation deals with duplicate client-provided
95 * hash values by chaining: the second and subsequent cmap_nodes with a given
96 * hash are chained off the initially inserted node's 'next' member. The hash
97 * table maintains the invariant that a single client-provided hash value
98 * exists in only a single chain in a single bucket (even though that hash
99 * could be stored in two buckets).
105 * [1] D. Zhou, B. Fan, H. Lim, M. Kaminsky, D. G. Andersen, "Scalable, High
106 * Performance Ethernet Forwarding with CuckooSwitch". In Proc. 9th
109 * [2] B. Fan, D. G. Andersen, and M. Kaminsky. "MemC3: Compact and concurrent
110 * memcache with dumber caching and smarter hashing". In Proc. 10th USENIX
113 * [3] R. Pagh and F. Rodler. "Cuckoo hashing". Journal of Algorithms, 51(2):
116 * [4] U. Erlingsson, M. Manasse, F. McSherry, "A Cool and Practical
117 * Alternative to Traditional Hash Tables". In Proc. 7th Workshop on
118 * Distributed Data and Structures (WDAS'06), 2006.
120 /* An entry is an int and a pointer: 8 bytes on 32-bit, 12 bytes on 64-bit. */
121 #define CMAP_ENTRY_SIZE (4 + (UINTPTR_MAX == UINT32_MAX ? 4 : 8))
123 /* Number of entries per bucket: 7 on 32-bit, 5 on 64-bit. */
124 #define CMAP_K ((CACHE_LINE_SIZE - 4) / CMAP_ENTRY_SIZE)
126 /* Pad to make a bucket a full cache line in size: 4 on 32-bit, 0 on 64-bit. */
127 #define CMAP_PADDING ((CACHE_LINE_SIZE - 4) - (CMAP_K * CMAP_ENTRY_SIZE))
129 /* A cuckoo hash bucket. Designed to be cache-aligned and exactly one cache
132 /* Allows readers to track in-progress changes. Initially zero, each
133 * writer increments this value just before and just after each change (see
134 * cmap_set_bucket()). Thus, a reader can ensure that it gets a consistent
135 * snapshot by waiting for the counter to become even (see
136 * read_even_counter()), then checking that its value does not change while
137 * examining the bucket (see cmap_find()). */
138 atomic_uint32_t counter;
140 /* (hash, node) slots. They are parallel arrays instead of an array of
141 * structs to reduce the amount of space lost to padding.
143 * The slots are in no particular order. A null pointer indicates that a
144 * pair is unused. In-use slots are not necessarily in the earliest
146 uint32_t hashes[CMAP_K];
147 struct cmap_node nodes[CMAP_K];
149 /* Padding to make cmap_bucket exactly one cache line long. */
151 uint8_t pad[CMAP_PADDING];
154 BUILD_ASSERT_DECL(sizeof(struct cmap_bucket) == CACHE_LINE_SIZE);
156 /* Default maximum load factor (as a fraction of UINT32_MAX + 1) before
157 * enlarging a cmap. Reasonable values lie between about 75% and 93%. Smaller
158 * values waste memory; larger values increase the average insertion time. */
159 #define CMAP_MAX_LOAD ((uint32_t) (UINT32_MAX * .85))
161 /* Default minimum load factor (as a fraction of UINT32_MAX + 1) before
162 * shrinking a cmap. Currently, the value is chosen to be 20%, this
163 * means cmap will have a 40% load factor after shrink. */
164 #define CMAP_MIN_LOAD ((uint32_t) (UINT32_MAX * .20))
166 /* The implementation of a concurrent hash map. */
168 unsigned int n; /* Number of in-use elements. */
169 unsigned int max_n; /* Max elements before enlarging. */
170 unsigned int min_n; /* Min elements before shrinking. */
171 uint32_t mask; /* Number of 'buckets', minus one. */
172 uint32_t basis; /* Basis for rehashing client's hash values. */
173 uint8_t pad[CACHE_LINE_SIZE - 4 * 5]; /* Pad to end of cache line. */
174 struct cmap_bucket buckets[1];
176 BUILD_ASSERT_DECL(sizeof(struct cmap_impl) == CACHE_LINE_SIZE * 2);
179 OVS_ALIGNED_VAR(CACHE_LINE_SIZE) const struct cmap_impl empty_cmap;
181 static struct cmap_impl *cmap_rehash(struct cmap *, uint32_t mask);
183 /* Explicit inline keywords in utility functions seem to be necessary
184 * to prevent performance regression on cmap_find(). */
186 /* Given a rehashed value 'hash', returns the other hash for that rehashed
187 * value. This is symmetric: other_hash(other_hash(x)) == x. (See also "Hash
188 * Functions" at the top of this file.) */
189 static inline uint32_t
190 other_hash(uint32_t hash)
192 return (hash << 16) | (hash >> 16);
195 /* Returns the rehashed value for 'hash' within 'impl'. (See also "Hash
196 * Functions" at the top of this file.) */
197 static inline uint32_t
198 rehash(const struct cmap_impl *impl, uint32_t hash)
200 return hash_finish(impl->basis, hash);
203 /* Not always without the inline keyword. */
204 static inline struct cmap_impl *
205 cmap_get_impl(const struct cmap *cmap)
207 return ovsrcu_get(struct cmap_impl *, &cmap->impl);
211 calc_max_n(uint32_t mask)
213 return ((uint64_t) (mask + 1) * CMAP_K * CMAP_MAX_LOAD) >> 32;
217 calc_min_n(uint32_t mask)
219 return ((uint64_t) (mask + 1) * CMAP_K * CMAP_MIN_LOAD) >> 32;
222 static struct cmap_impl *
223 cmap_impl_create(uint32_t mask)
225 struct cmap_impl *impl;
227 ovs_assert(is_pow2(mask + 1));
229 /* There are 'mask + 1' buckets but struct cmap_impl has one bucket built
230 * in, so we only need to add space for the extra 'mask' buckets. */
231 impl = xzalloc_cacheline(sizeof *impl + mask * sizeof *impl->buckets);
233 impl->max_n = calc_max_n(mask);
234 impl->min_n = calc_min_n(mask);
236 impl->basis = random_uint32();
241 /* Initializes 'cmap' as an empty concurrent hash map. */
243 cmap_init(struct cmap *cmap)
245 ovsrcu_set(&cmap->impl, CONST_CAST(struct cmap_impl *, &empty_cmap));
250 * The client is responsible for destroying any data previously held in
253 cmap_destroy(struct cmap *cmap)
256 struct cmap_impl *impl = cmap_get_impl(cmap);
257 if (impl != &empty_cmap) {
258 ovsrcu_postpone(free_cacheline, impl);
263 /* Returns the number of elements in 'cmap'. */
265 cmap_count(const struct cmap *cmap)
267 return cmap_get_impl(cmap)->n;
270 /* Returns true if 'cmap' is empty, false otherwise. */
272 cmap_is_empty(const struct cmap *cmap)
274 return cmap_count(cmap) == 0;
277 static inline uint32_t
278 read_counter(const struct cmap_bucket *bucket_)
280 struct cmap_bucket *bucket = CONST_CAST(struct cmap_bucket *, bucket_);
283 atomic_read_explicit(&bucket->counter, &counter, memory_order_acquire);
288 static inline uint32_t
289 read_even_counter(const struct cmap_bucket *bucket)
294 counter = read_counter(bucket);
295 } while (OVS_UNLIKELY(counter & 1));
301 counter_changed(const struct cmap_bucket *b_, uint32_t c)
303 struct cmap_bucket *b = CONST_CAST(struct cmap_bucket *, b_);
306 /* Need to make sure the counter read is not moved up, before the hash and
307 * cmap_node_next(). Using atomic_read_explicit with memory_order_acquire
308 * would allow prior reads to be moved after the barrier.
309 * atomic_thread_fence prevents all following memory accesses from moving
310 * prior to preceding loads. */
311 atomic_thread_fence(memory_order_acquire);
312 atomic_read_relaxed(&b->counter, &counter);
314 return OVS_UNLIKELY(counter != c);
317 static inline const struct cmap_node *
318 cmap_find_in_bucket(const struct cmap_bucket *bucket, uint32_t hash)
320 for (int i = 0; i < CMAP_K; i++) {
321 if (bucket->hashes[i] == hash) {
322 return cmap_node_next(&bucket->nodes[i]);
328 static inline const struct cmap_node *
329 cmap_find__(const struct cmap_bucket *b1, const struct cmap_bucket *b2,
333 const struct cmap_node *node;
337 c1 = read_even_counter(b1);
338 node = cmap_find_in_bucket(b1, hash);
339 } while (OVS_UNLIKELY(counter_changed(b1, c1)));
344 c2 = read_even_counter(b2);
345 node = cmap_find_in_bucket(b2, hash);
346 } while (OVS_UNLIKELY(counter_changed(b2, c2)));
350 } while (OVS_UNLIKELY(counter_changed(b1, c1)));
355 /* Searches 'cmap' for an element with the specified 'hash'. If one or more is
356 * found, returns a pointer to the first one, otherwise a null pointer. All of
357 * the nodes on the returned list are guaranteed to have exactly the given
360 * This function works even if 'cmap' is changing concurrently. If 'cmap' is
361 * not changing, then cmap_find_protected() is slightly faster.
363 * CMAP_FOR_EACH_WITH_HASH is usually more convenient. */
364 const struct cmap_node *
365 cmap_find(const struct cmap *cmap, uint32_t hash)
367 const struct cmap_impl *impl = cmap_get_impl(cmap);
368 uint32_t h1 = rehash(impl, hash);
369 uint32_t h2 = other_hash(h1);
371 return cmap_find__(&impl->buckets[h1 & impl->mask],
372 &impl->buckets[h2 & impl->mask],
376 /* Looks up multiple 'hashes', when the corresponding bit in 'map' is 1,
377 * and sets the corresponding pointer in 'nodes', if the hash value was
378 * found from the 'cmap'. In other cases the 'nodes' values are not changed,
379 * i.e., no NULL pointers are stored there.
380 * Returns a map where a bit is set to 1 if the corresponding 'nodes' pointer
381 * was stored, 0 otherwise.
382 * Generally, the caller wants to use CMAP_NODE_FOR_EACH to verify for
383 * hash collisions. */
385 cmap_find_batch(const struct cmap *cmap, unsigned long map,
386 uint32_t hashes[], const struct cmap_node *nodes[])
388 const struct cmap_impl *impl = cmap_get_impl(cmap);
389 unsigned long result = map;
391 uint32_t h1s[sizeof map * CHAR_BIT];
392 const struct cmap_bucket *b1s[sizeof map * CHAR_BIT];
393 const struct cmap_bucket *b2s[sizeof map * CHAR_BIT];
394 uint32_t c1s[sizeof map * CHAR_BIT];
396 /* Compute hashes and prefetch 1st buckets. */
397 ULLONG_FOR_EACH_1(i, map) {
398 h1s[i] = rehash(impl, hashes[i]);
399 b1s[i] = &impl->buckets[h1s[i] & impl->mask];
400 OVS_PREFETCH(b1s[i]);
402 /* Lookups, Round 1. Only look up at the first bucket. */
403 ULLONG_FOR_EACH_1(i, map) {
405 const struct cmap_bucket *b1 = b1s[i];
406 const struct cmap_node *node;
409 c1 = read_even_counter(b1);
410 node = cmap_find_in_bucket(b1, hashes[i]);
411 } while (OVS_UNLIKELY(counter_changed(b1, c1)));
414 /* Not found (yet); Prefetch the 2nd bucket. */
415 b2s[i] = &impl->buckets[other_hash(h1s[i]) & impl->mask];
416 OVS_PREFETCH(b2s[i]);
417 c1s[i] = c1; /* We may need to check this after Round 2. */
421 ULLONG_SET0(map, i); /* Ignore this on round 2. */
425 /* Round 2. Look into the 2nd bucket, if needed. */
426 ULLONG_FOR_EACH_1(i, map) {
428 const struct cmap_bucket *b2 = b2s[i];
429 const struct cmap_node *node;
432 c2 = read_even_counter(b2);
433 node = cmap_find_in_bucket(b2, hashes[i]);
434 } while (OVS_UNLIKELY(counter_changed(b2, c2)));
437 /* Not found, but the node may have been moved from b2 to b1 right
438 * after we finished with b1 earlier. We just got a clean reading
439 * of the 2nd bucket, so we check the counter of the 1st bucket
440 * only. However, we need to check both buckets again, as the
441 * entry may be moved again to the 2nd bucket. Basically, we
442 * need to loop as long as it takes to get stable readings of
443 * both buckets. cmap_find__() does that, and now that we have
444 * fetched both buckets we can just use it. */
445 if (OVS_UNLIKELY(counter_changed(b1s[i], c1s[i]))) {
446 node = cmap_find__(b1s[i], b2s[i], hashes[i]);
452 ULLONG_SET0(result, i); /* Fix the result. */
463 cmap_find_slot_protected(struct cmap_bucket *b, uint32_t hash)
467 for (i = 0; i < CMAP_K; i++) {
468 if (b->hashes[i] == hash && cmap_node_next_protected(&b->nodes[i])) {
475 static struct cmap_node *
476 cmap_find_bucket_protected(struct cmap_impl *impl, uint32_t hash, uint32_t h)
478 struct cmap_bucket *b = &impl->buckets[h & impl->mask];
481 for (i = 0; i < CMAP_K; i++) {
482 if (b->hashes[i] == hash) {
483 return cmap_node_next_protected(&b->nodes[i]);
489 /* Like cmap_find(), but only for use if 'cmap' cannot change concurrently.
491 * CMAP_FOR_EACH_WITH_HASH_PROTECTED is usually more convenient. */
493 cmap_find_protected(const struct cmap *cmap, uint32_t hash)
495 struct cmap_impl *impl = cmap_get_impl(cmap);
496 uint32_t h1 = rehash(impl, hash);
497 uint32_t h2 = other_hash(hash);
498 struct cmap_node *node;
500 node = cmap_find_bucket_protected(impl, hash, h1);
504 return cmap_find_bucket_protected(impl, hash, h2);
508 cmap_find_empty_slot_protected(const struct cmap_bucket *b)
512 for (i = 0; i < CMAP_K; i++) {
513 if (!cmap_node_next_protected(&b->nodes[i])) {
521 cmap_set_bucket(struct cmap_bucket *b, int i,
522 struct cmap_node *node, uint32_t hash)
526 atomic_read_explicit(&b->counter, &c, memory_order_acquire);
527 atomic_store_explicit(&b->counter, c + 1, memory_order_release);
528 ovsrcu_set(&b->nodes[i].next, node); /* Also atomic. */
530 atomic_store_explicit(&b->counter, c + 2, memory_order_release);
533 /* Searches 'b' for a node with the given 'hash'. If it finds one, adds
534 * 'new_node' to the node's linked list and returns true. If it does not find
535 * one, returns false. */
537 cmap_insert_dup(struct cmap_node *new_node, uint32_t hash,
538 struct cmap_bucket *b)
542 for (i = 0; i < CMAP_K; i++) {
543 if (b->hashes[i] == hash) {
544 struct cmap_node *node = cmap_node_next_protected(&b->nodes[i]);
549 /* The common case is that 'new_node' is a singleton,
550 * with a null 'next' pointer. Rehashing can add a
551 * longer chain, but due to our invariant of always
552 * having all nodes with the same (user) hash value at
553 * a single chain, rehashing will always insert the
554 * chain to an empty node. The only way we can end up
555 * here is by the user inserting a chain of nodes at
556 * once. Find the end of the chain starting at
557 * 'new_node', then splice 'node' to the end of that
561 struct cmap_node *next = cmap_node_next_protected(p);
568 ovsrcu_set_hidden(&p->next, node);
570 /* The hash value is there from some previous insertion, but
571 * the associated node has been removed. We're not really
572 * inserting a duplicate, but we can still reuse the slot.
576 /* Change the bucket to point to 'new_node'. This is a degenerate
577 * form of cmap_set_bucket() that doesn't update the counter since
578 * we're only touching one field and in a way that doesn't change
579 * the bucket's meaning for readers. */
580 ovsrcu_set(&b->nodes[i].next, new_node);
588 /* Searches 'b' for an empty slot. If successful, stores 'node' and 'hash' in
589 * the slot and returns true. Otherwise, returns false. */
591 cmap_insert_bucket(struct cmap_node *node, uint32_t hash,
592 struct cmap_bucket *b)
596 for (i = 0; i < CMAP_K; i++) {
597 if (!cmap_node_next_protected(&b->nodes[i])) {
598 cmap_set_bucket(b, i, node, hash);
605 /* Returns the other bucket that b->nodes[slot] could occupy in 'impl'. (This
606 * might be the same as 'b'.) */
607 static struct cmap_bucket *
608 other_bucket_protected(struct cmap_impl *impl, struct cmap_bucket *b, int slot)
610 uint32_t h1 = rehash(impl, b->hashes[slot]);
611 uint32_t h2 = other_hash(h1);
612 uint32_t b_idx = b - impl->buckets;
613 uint32_t other_h = (h1 & impl->mask) == b_idx ? h2 : h1;
615 return &impl->buckets[other_h & impl->mask];
618 /* 'new_node' is to be inserted into 'impl', but both candidate buckets 'b1'
619 * and 'b2' are full. This function attempts to rearrange buckets within
620 * 'impl' to make room for 'new_node'.
622 * The implementation is a general-purpose breadth-first search. At first
623 * glance, this is more complex than a random walk through 'impl' (suggested by
624 * some references), but random walks have a tendency to loop back through a
625 * single bucket. We have to move nodes backward along the path that we find,
626 * so that no node actually disappears from the hash table, which means a
627 * random walk would have to be careful to deal with loops. By contrast, a
628 * successful breadth-first search always finds a *shortest* path through the
629 * hash table, and a shortest path will never contain loops, so it avoids that
633 cmap_insert_bfs(struct cmap_impl *impl, struct cmap_node *new_node,
634 uint32_t hash, struct cmap_bucket *b1, struct cmap_bucket *b2)
636 enum { MAX_DEPTH = 4 };
638 /* A path from 'start' to 'end' via the 'n' steps in 'slots[]'.
640 * One can follow the path via:
642 * struct cmap_bucket *b;
646 * for (i = 0; i < path->n; i++) {
647 * b = other_bucket_protected(impl, b, path->slots[i]);
649 * ovs_assert(b == path->end);
652 struct cmap_bucket *start; /* First bucket along the path. */
653 struct cmap_bucket *end; /* Last bucket on the path. */
654 uint8_t slots[MAX_DEPTH]; /* Slots used for each hop. */
655 int n; /* Number of slots[]. */
658 /* We need to limit the amount of work we do trying to find a path. It
659 * might actually be impossible to rearrange the cmap, and after some time
660 * it is likely to be easier to rehash the entire cmap.
662 * This value of MAX_QUEUE is an arbitrary limit suggested by one of the
663 * references. Empirically, it seems to work OK. */
664 enum { MAX_QUEUE = 500 };
665 struct cmap_path queue[MAX_QUEUE];
669 /* Add 'b1' and 'b2' as starting points for the search. */
670 queue[head].start = b1;
671 queue[head].end = b1;
675 queue[head].start = b2;
676 queue[head].end = b2;
681 while (tail < head) {
682 const struct cmap_path *path = &queue[tail++];
683 struct cmap_bucket *this = path->end;
686 for (i = 0; i < CMAP_K; i++) {
687 struct cmap_bucket *next = other_bucket_protected(impl, this, i);
694 j = cmap_find_empty_slot_protected(next);
696 /* We've found a path along which we can rearrange the hash
697 * table: Start at path->start, follow all the slots in
698 * path->slots[], then follow slot 'i', then the bucket you
699 * arrive at has slot 'j' empty. */
700 struct cmap_bucket *buckets[MAX_DEPTH + 2];
701 int slots[MAX_DEPTH + 2];
704 /* Figure out the full sequence of slots. */
705 for (k = 0; k < path->n; k++) {
706 slots[k] = path->slots[k];
709 slots[path->n + 1] = j;
711 /* Figure out the full sequence of buckets. */
712 buckets[0] = path->start;
713 for (k = 0; k <= path->n; k++) {
714 buckets[k + 1] = other_bucket_protected(impl, buckets[k], slots[k]);
717 /* Now the path is fully expressed. One can start from
718 * buckets[0], go via slots[0] to buckets[1], via slots[1] to
719 * buckets[2], and so on.
721 * Move all the nodes across the path "backward". After each
722 * step some node appears in two buckets. Thus, every node is
723 * always visible to a concurrent search. */
724 for (k = path->n + 1; k > 0; k--) {
725 int slot = slots[k - 1];
728 buckets[k], slots[k],
729 cmap_node_next_protected(&buckets[k - 1]->nodes[slot]),
730 buckets[k - 1]->hashes[slot]);
733 /* Finally, replace the first node on the path by
735 cmap_set_bucket(buckets[0], slots[0], new_node, hash);
740 if (path->n < MAX_DEPTH && head < MAX_QUEUE) {
741 struct cmap_path *new_path = &queue[head++];
744 new_path->end = next;
745 new_path->slots[new_path->n++] = i;
753 /* Adds 'node', with the given 'hash', to 'impl'.
755 * 'node' is ordinarily a single node, with a null 'next' pointer. When
756 * rehashing, however, it may be a longer chain of nodes. */
758 cmap_try_insert(struct cmap_impl *impl, struct cmap_node *node, uint32_t hash)
760 uint32_t h1 = rehash(impl, hash);
761 uint32_t h2 = other_hash(h1);
762 struct cmap_bucket *b1 = &impl->buckets[h1 & impl->mask];
763 struct cmap_bucket *b2 = &impl->buckets[h2 & impl->mask];
765 return (OVS_UNLIKELY(cmap_insert_dup(node, hash, b1) ||
766 cmap_insert_dup(node, hash, b2)) ||
767 OVS_LIKELY(cmap_insert_bucket(node, hash, b1) ||
768 cmap_insert_bucket(node, hash, b2)) ||
769 cmap_insert_bfs(impl, node, hash, b1, b2));
772 /* Inserts 'node', with the given 'hash', into 'cmap'. The caller must ensure
773 * that 'cmap' cannot change concurrently (from another thread). If duplicates
774 * are undesirable, the caller must have already verified that 'cmap' does not
775 * contain a duplicate of 'node'.
777 * Returns the current number of nodes in the cmap after the insertion. */
779 cmap_insert(struct cmap *cmap, struct cmap_node *node, uint32_t hash)
781 struct cmap_impl *impl = cmap_get_impl(cmap);
783 ovsrcu_set_hidden(&node->next, NULL);
785 if (OVS_UNLIKELY(impl->n >= impl->max_n)) {
786 COVERAGE_INC(cmap_expand);
787 impl = cmap_rehash(cmap, (impl->mask << 1) | 1);
790 while (OVS_UNLIKELY(!cmap_try_insert(impl, node, hash))) {
791 impl = cmap_rehash(cmap, impl->mask);
797 cmap_replace__(struct cmap_impl *impl, struct cmap_node *node,
798 struct cmap_node *replacement, uint32_t hash, uint32_t h)
800 struct cmap_bucket *b = &impl->buckets[h & impl->mask];
803 slot = cmap_find_slot_protected(b, hash);
808 /* The pointer to 'node' is changed to point to 'replacement',
809 * which is the next node if no replacement node is given. */
811 replacement = cmap_node_next_protected(node);
813 /* 'replacement' takes the position of 'node' in the list. */
814 ovsrcu_set_hidden(&replacement->next, cmap_node_next_protected(node));
817 struct cmap_node *iter = &b->nodes[slot];
819 struct cmap_node *next = cmap_node_next_protected(iter);
822 ovsrcu_set(&iter->next, replacement);
829 /* Replaces 'old_node' in 'cmap' with 'new_node'. The caller must
830 * ensure that 'cmap' cannot change concurrently (from another thread).
832 * 'old_node' must not be destroyed or modified or inserted back into 'cmap' or
833 * into any other concurrent hash map while any other thread might be accessing
834 * it. One correct way to do this is to free it from an RCU callback with
837 * Returns the current number of nodes in the cmap after the replacement. The
838 * number of nodes decreases by one if 'new_node' is NULL. */
840 cmap_replace(struct cmap *cmap, struct cmap_node *old_node,
841 struct cmap_node *new_node, uint32_t hash)
843 struct cmap_impl *impl = cmap_get_impl(cmap);
844 uint32_t h1 = rehash(impl, hash);
845 uint32_t h2 = other_hash(h1);
848 ok = cmap_replace__(impl, old_node, new_node, hash, h1)
849 || cmap_replace__(impl, old_node, new_node, hash, h2);
854 if (OVS_UNLIKELY(impl->n < impl->min_n)) {
855 COVERAGE_INC(cmap_shrink);
856 impl = cmap_rehash(cmap, impl->mask >> 1);
863 cmap_try_rehash(const struct cmap_impl *old, struct cmap_impl *new)
865 const struct cmap_bucket *b;
867 for (b = old->buckets; b <= &old->buckets[old->mask]; b++) {
870 for (i = 0; i < CMAP_K; i++) {
871 /* possible optimization here because we know the hashes are
873 struct cmap_node *node = cmap_node_next_protected(&b->nodes[i]);
875 if (node && !cmap_try_insert(new, node, b->hashes[i])) {
883 static struct cmap_impl *
884 cmap_rehash(struct cmap *cmap, uint32_t mask)
886 struct cmap_impl *old = cmap_get_impl(cmap);
887 struct cmap_impl *new;
889 new = cmap_impl_create(mask);
890 ovs_assert(old->n < new->max_n);
892 while (!cmap_try_rehash(old, new)) {
893 memset(new->buckets, 0, (mask + 1) * sizeof *new->buckets);
894 new->basis = random_uint32();
898 ovsrcu_set(&cmap->impl, new);
899 if (old != &empty_cmap) {
900 ovsrcu_postpone(free_cacheline, old);
907 cmap_cursor_start(const struct cmap *cmap)
909 struct cmap_cursor cursor;
911 cursor.impl = cmap_get_impl(cmap);
912 cursor.bucket_idx = 0;
913 cursor.entry_idx = 0;
915 cmap_cursor_advance(&cursor);
921 cmap_cursor_advance(struct cmap_cursor *cursor)
923 const struct cmap_impl *impl = cursor->impl;
926 cursor->node = cmap_node_next(cursor->node);
932 while (cursor->bucket_idx <= impl->mask) {
933 const struct cmap_bucket *b = &impl->buckets[cursor->bucket_idx];
935 while (cursor->entry_idx < CMAP_K) {
936 cursor->node = cmap_node_next(&b->nodes[cursor->entry_idx++]);
942 cursor->bucket_idx++;
943 cursor->entry_idx = 0;
947 /* Returns the next node in 'cmap' in hash order, or NULL if no nodes remain in
948 * 'cmap'. Uses '*pos' to determine where to begin iteration, and updates
949 * '*pos' to pass on the next iteration into them before returning.
951 * It's better to use plain CMAP_FOR_EACH and related functions, since they are
952 * faster and better at dealing with cmaps that change during iteration.
954 * Before beginning iteration, set '*pos' to all zeros. */
956 cmap_next_position(const struct cmap *cmap,
957 struct cmap_position *pos)
959 struct cmap_impl *impl = cmap_get_impl(cmap);
960 unsigned int bucket = pos->bucket;
961 unsigned int entry = pos->entry;
962 unsigned int offset = pos->offset;
964 while (bucket <= impl->mask) {
965 const struct cmap_bucket *b = &impl->buckets[bucket];
967 while (entry < CMAP_K) {
968 const struct cmap_node *node = cmap_node_next(&b->nodes[entry]);
971 for (i = 0; node; i++, node = cmap_node_next(node)) {
973 if (cmap_node_next(node)) {
979 pos->bucket = bucket;
981 pos->offset = offset;
982 return CONST_CAST(struct cmap_node *, node);
994 pos->bucket = pos->entry = pos->offset = 0;