This is a fast, scalable chained hash table with optional auto-resizing,
allowing
reads that are concurrent with reads, and reads/writes that are concurrent
with writes to separate buckets.
A hash table with these features will be necessary for the scalability
of the ongoing MTTCG work; before those changes arrive we can already
benefit from the single-threaded speedup that qht also provides.
Reviewed-by: Richard Henderson <r...@twiddle.net>
Signed-off-by: Emilio G. Cota <c...@braap.org>
---
include/qemu/qht.h | 66 +++++
util/Makefile.objs | 1 +
util/qht.c | 703 +++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 770 insertions(+)
create mode 100644 include/qemu/qht.h
create mode 100644 util/qht.c
diff --git a/include/qemu/qht.h b/include/qemu/qht.h
new file mode 100644
index 0000000..c2ab8b8
--- /dev/null
+++ b/include/qemu/qht.h
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2016, Emilio G. Cota <c...@braap.org>
+ *
+ * License: GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#ifndef QEMU_QHT_H
+#define QEMU_QHT_H
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qemu/seqlock.h"
+#include "qemu/qdist.h"
+#include "qemu/rcu.h"
+
+struct qht {
+ struct qht_map *map;
+ unsigned int mode;
+};
+
+struct qht_stats {
+ size_t head_buckets;
+ size_t used_head_buckets;
+ size_t entries;
+ struct qdist chain;
+ struct qdist occupancy;
+};
+
+typedef bool (*qht_lookup_func_t)(const void *obj, const void *userp);
+typedef void (*qht_iter_func_t)(struct qht *ht, void *p, uint32_t h, void *up);
+
+#define QHT_MODE_AUTO_RESIZE 0x1 /* auto-resize when heavily loaded */
+
+void qht_init(struct qht *ht, size_t n_elems, unsigned int mode);
+
+/* call only when there are no readers left */
+void qht_destroy(struct qht *ht);
+
+/* call with an external lock held */
+void qht_reset(struct qht *ht);
+
+/* call with an external lock held */
+bool qht_reset_size(struct qht *ht, size_t n_elems);
+
+/* call with an external lock held */
+bool qht_insert(struct qht *ht, void *p, uint32_t hash);
+
+/* call with an external lock held */
+bool qht_remove(struct qht *ht, const void *p, uint32_t hash);
+
+/* call with an external lock held */
+void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp);
+
+/* call with an external lock held */
+bool qht_resize(struct qht *ht, size_t n_elems);
+
+/* if @func is NULL, then pointer comparison is used */
+void *qht_lookup(struct qht *ht, qht_lookup_func_t func, const void *userp,
+ uint32_t hash);
+
+/* pass @stats to qht_statistics_destroy() when done */
+void qht_statistics_init(struct qht *ht, struct qht_stats *stats);
+
+void qht_statistics_destroy(struct qht_stats *stats);
+
+#endif /* QEMU_QHT_H */
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 702435e..45f8794 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -33,3 +33,4 @@ util-obj-y += timed-average.o
util-obj-y += base64.o
util-obj-y += log.o
util-obj-y += qdist.o
+util-obj-y += qht.o
diff --git a/util/qht.c b/util/qht.c
new file mode 100644
index 0000000..112f32d
--- /dev/null
+++ b/util/qht.c
@@ -0,0 +1,703 @@
+/*
+ * qht.c - QEMU Hash Table, designed to scale for read-mostly workloads.
+ *
+ * Copyright (C) 2016, Emilio G. Cota <c...@braap.org>
+ *
+ * License: GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ * Assumptions:
+ * - Writers and iterators must take an external lock.
+ * - NULL cannot be inserted as a pointer value.
+ * - Duplicate pointer values cannot be inserted.
+ *
+ * Features:
+ * - Optional auto-resizing: the hash table resizes up if the load surpasses
+ * a certain threshold. Resizing is done concurrently with readers.
+ *
+ * The key structure is the bucket, which is cacheline-sized. Buckets
+ * contain a few hash values and pointers; the u32 hash values are stored in
+ * full so that resizing is fast. Having this structure instead of directly
+ * chaining items has three advantages:
+ * - Failed lookups fail fast, and touch a minimum number of cache lines.
+ * - Resizing the hash table with concurrent lookups is easy.
+ *
+ * There are two types of buckets:
+ * 1. "head" buckets are the ones allocated in the array of buckets in qht_map.
+ * 2. all "non-head" buckets (i.e. all others) are members of a chain that
+ * starts from a head bucket.
+ * Note that the seqlock and spinlock of a head bucket applies to all buckets
+ * chained to it; these two fields are unused in non-head buckets.
+ *
+ * On removals, we move the last valid item in the chain to the position of the
+ * just-removed entry. This makes lookups slightly faster, since the moment an
+ * invalid entry is found, the (failed) lookup is over.
+ *
+ * Resizing is done by taking all spinlocks (so that no readers-turned-writers
+ * can race with us) and then placing all elements into a new hash table. Last,
+ * the ht->map pointer is set, and the old map is freed once no RCU readers can
+ * see it anymore.
+ *
+ * Related Work:
+ * - Idea of cacheline-sized buckets with full hashes taken from:
+ * David, Guerraoui & Trigonakis, "Asynchronized Concurrency:
+ * The Secret to Scaling Concurrent Search Data Structures", ASPLOS'15.
+ * - Why not RCU-based hash tables? They would allow us to get rid of the
+ * seqlock, but resizing would take forever since RCU read critical
+ * sections in QEMU take quite a long time.
+ * More info on relativistic hash tables:
+ * + Triplett, McKenney & Walpole, "Resizable, Scalable, Concurrent Hash
+ * Tables via Relativistic Programming", USENIX ATC'11.
+ * + Corbet, "Relativistic hash tables, part 1: Algorithms", @ lwn.net, 2014.
+ * https://lwn.net/Articles/612021/
+ */
+#include "qemu/qht.h"
+#include "qemu/atomic.h"
+
+//#define QHT_DEBUG
+
+/*
+ * We want to avoid false sharing of cache lines. Most systems have 64-byte
+ * cache lines so we go with it for simplicity.
+ *
+ * Note that systems with smaller cache lines will be fine (the struct is
+ * almost 64-bytes); systems with larger cache lines might suffer from
+ * some false sharing.
+ */
+#define QHT_BUCKET_ALIGN 64
+
+/* define these to keep sizeof(qht_bucket) within QHT_BUCKET_ALIGN */
+#if HOST_LONG_BITS == 32
+#define QHT_BUCKET_ENTRIES 6
+#else /* 64-bit */
+#define QHT_BUCKET_ENTRIES 4
+#endif
+
+struct qht_bucket {
+ QemuSpin lock;
+ QemuSeqLock sequence;
+ uint32_t hashes[QHT_BUCKET_ENTRIES];
+ void *pointers[QHT_BUCKET_ENTRIES];
+ struct qht_bucket *next;
+} QEMU_ALIGNED(QHT_BUCKET_ALIGN);
+
+QEMU_BUILD_BUG_ON(sizeof(struct qht_bucket) > QHT_BUCKET_ALIGN);
+
+/**
+ * struct qht_map - structure to track an array of buckets
+ * @rcu: used by RCU. Keep it as the top field in the struct to help valgrind
+ * find the whole struct.
+ * @buckets: array of head buckets. It is constant once the map is created.
+ * @n: number of head buckets. It is constant once the map is created.
+ * @n_added_buckets: number of added (i.e. "non-head") buckets
+ * @n_added_buckets_threshold: threshold to trigger an upward resize once the
+ * number of added buckets surpasses it.
+ *
+ * Buckets are tracked in what we call a "map", i.e. this structure.
+ */
+struct qht_map {
+ struct rcu_head rcu;
+ struct qht_bucket *buckets;
+ size_t n;
+ size_t n_added_buckets;
+ size_t n_added_buckets_threshold;
+};
+
+/* trigger a resize when n_added_buckets > n_buckets / div */
+#define QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV 8
+
+static void qht_do_resize(struct qht *ht, size_t n);
+
+static inline struct qht_map *qht_map__atomic_mb(const struct qht *ht)
+{
+ struct qht_map *map;
+
+ map = atomic_read(&ht->map);
+ /* paired with smp_wmb() before setting ht->map */
+ smp_rmb();
+ return map;
+}
+
+/* helper for lockless bucket chain traversals */
+static inline
+struct qht_bucket *bucket_next__atomic_mb(const struct qht_bucket *b)
+{
+ struct qht_bucket *ret;
+
+ ret = atomic_read(&b->next);
+ /*
+ * This barrier guarantees that we will read a properly initialized
b->next;
+ * it is paired with an smp_wmb() before setting b->next.
+ */
+ smp_rmb();
+ return ret;
+}
+
+#ifdef QHT_DEBUG
+static void qht_bucket_debug(struct qht_bucket *b)
+{
+ bool seen_empty = false;
+ bool corrupt = false;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ seen_empty = true;
+ continue;
+ }
+ if (seen_empty) {
+ fprintf(stderr, "%s: b: %p, pos: %i, hash: 0x%x, p: %p\n",
+ __func__, b, i, b->hashes[i], b->pointers[i]);
+ corrupt = true;
+ }
+ }
+ b = b->next;
+ } while (b);
+ assert(!corrupt);
+}
+
+static void qht_map_debug(struct qht_map *map)
+{
+ int i;
+
+ for (i = 0; i < map->n; i++) {
+ qht_bucket_debug(&map->buckets[i]);
+ }
+}
+#else
+static inline void qht_bucket_debug(struct qht_bucket *b)
+{ }
+
+static inline void qht_map_debug(struct qht_map *map)
+{ }
+#endif /* QHT_DEBUG */
+
+static inline size_t qht_elems_to_buckets(size_t n_elems)
+{
+ return pow2ceil(n_elems / QHT_BUCKET_ENTRIES);
+}
+
+static inline void qht_head_init(struct qht_bucket *b)
+{
+ memset(b, 0, sizeof(*b));
+ qemu_spin_init(&b->lock);
+ seqlock_init(&b->sequence);
+}
+
+static inline
+struct qht_bucket *qht_map_to_bucket(struct qht_map *map, uint32_t hash)
+{
+ return &map->buckets[hash & (map->n - 1)];
+}
+
+/* acquire all bucket locks from a map */
+static void qht_map_lock_buckets(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n; i++) {
+ struct qht_bucket *b = &map->buckets[i];
+
+ qemu_spin_lock(&b->lock);
+ }
+}
+
+static void qht_map_unlock_buckets(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n; i++) {
+ struct qht_bucket *b = &map->buckets[i];
+
+ qemu_spin_unlock(&b->lock);
+ }
+}
+
+static inline bool qht_map_needs_resize(struct qht_map *map)
+{
+ return atomic_read(&map->n_added_buckets) > map->n_added_buckets_threshold;
+}
+
+static inline void qht_chain_destroy(struct qht_bucket *head)
+{
+ struct qht_bucket *curr = head->next;
+ struct qht_bucket *prev;
+
+ while (curr) {
+ prev = curr;
+ curr = curr->next;
+ qemu_vfree(prev);
+ }
+}
+
+/* pass only an orphan map */
+static void qht_map_destroy(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n; i++) {
+ qht_chain_destroy(&map->buckets[i]);
+ }
+ qemu_vfree(map->buckets);
+ g_free(map);
+}
+
+static void qht_map_reclaim(struct rcu_head *rcu)
+{
+ struct qht_map *map = container_of(rcu, struct qht_map, rcu);
+
+ qht_map_destroy(map);
+}
+
+static struct qht_map *qht_map_create(size_t n)
+{
+ struct qht_map *map;
+ size_t i;
+
+ map = g_malloc(sizeof(*map));
+ map->n = n;
+
+ map->n_added_buckets = 0;
+ map->n_added_buckets_threshold = n / QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV;
+
+ /* let tiny hash tables to at least add one non-head bucket */
+ if (unlikely(map->n_added_buckets_threshold == 0)) {
+ map->n_added_buckets_threshold = 1;
+ }
+
+ map->buckets = qemu_memalign(QHT_BUCKET_ALIGN, sizeof(*map->buckets) * n);
+ for (i = 0; i < n; i++) {
+ qht_head_init(&map->buckets[i]);
+ }
+ return map;
+}
+
+static inline void qht_publish(struct qht *ht, struct qht_map *new)
+{
+ /* Readers should see a properly initialized map; pair with smp_rmb() */
+ smp_wmb();
+ atomic_set(&ht->map, new);
+}
+
+void qht_init(struct qht *ht, size_t n_elems, unsigned int mode)
+{
+ struct qht_map *map;
+ size_t n = qht_elems_to_buckets(n_elems);
+
+ ht->mode = mode;
+ map = qht_map_create(n);
+ qht_publish(ht, map);
+}
+
+/* call only when there are no readers left */
+void qht_destroy(struct qht *ht)
+{
+ qht_map_destroy(ht->map);
+ memset(ht, 0, sizeof(*ht));
+}
+
+static void qht_bucket_reset(struct qht_bucket *head)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ qemu_spin_lock(&head->lock);
+ seqlock_write_begin(&head->sequence);
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ goto done;
+ }
+ atomic_set(&b->hashes[i], 0);
+ atomic_set(&b->pointers[i], NULL);
+ }
+ b = b->next;
+ } while (b);
+ done:
+ seqlock_write_end(&head->sequence);
+ qemu_spin_unlock(&head->lock);
+}
+
+/* call with an external lock held */
+void qht_reset(struct qht *ht)
+{
+ struct qht_map *map = ht->map;
+ size_t i;
+
+ for (i = 0; i < map->n; i++) {
+ qht_bucket_reset(&map->buckets[i]);
+ }
+ qht_map_debug(map);
+}
+
+/* call with an external lock held */
+bool qht_reset_size(struct qht *ht, size_t n_elems)
+{
+ struct qht_map *old = ht->map;
+
+ qht_reset(ht);
+ if (old->n == qht_elems_to_buckets(n_elems)) {
+ return false;
+ }
+ qht_init(ht, n_elems, ht->mode);
+ call_rcu1(&old->rcu, qht_map_reclaim);
+ return true;
+}
+
+static inline
+void *qht_do_lookup(struct qht_bucket *head, qht_lookup_func_t func,
+ const void *userp, uint32_t hash)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (atomic_read(&b->hashes[i]) == hash) {
+ void *p = atomic_read(&b->pointers[i]);
+
+ if (likely(p) && likely(func(p, userp))) {
+ return p;
+ }
+ }
+ }
+ b = bucket_next__atomic_mb(b);
+ } while (b);
+
+ return NULL;
+}
+
+static __attribute__((noinline))
+void *qht_lookup__slowpath(struct qht_bucket *b, qht_lookup_func_t func,
+ const void *userp, uint32_t hash)
+{
+ uint32_t version;
+ void *ret;
+
+ do {
+ version = seqlock_read_begin(&b->sequence);
+ ret = qht_do_lookup(b, func, userp, hash);
+ } while (seqlock_read_retry(&b->sequence, version));
+ return ret;
+}
+
+void *qht_lookup(struct qht *ht, qht_lookup_func_t func, const void *userp,
+ uint32_t hash)
+{
+ struct qht_bucket *b;
+ struct qht_map *map;
+ uint32_t version;
+ void *ret;
+
+ map = qht_map__atomic_mb(ht);
+ b = qht_map_to_bucket(map, hash);
+
+ version = seqlock_read_begin(&b->sequence);
+ ret = qht_do_lookup(b, func, userp, hash);
+ if (likely(!seqlock_read_retry(&b->sequence, version))) {
+ return ret;
+ }
+ /*
+ * Removing the do/while from the fastpath gives a 4% perf. increase when
+ * running a 100%-lookup microbenchmark.
+ */
+ return qht_lookup__slowpath(b, func, userp, hash);
+}
+
+/* call with head->lock held */
+static bool qht_insert__locked(struct qht *ht, struct qht_map *map,
+ struct qht_bucket *head, void *p, uint32_t hash,
+ bool *needs_resize)
+{
+ struct qht_bucket *b = head;
+ struct qht_bucket *prev = NULL;
+ struct qht_bucket *new = NULL;
+ int i;
+
+ for (;;) {
+ if (b == NULL) {
+ b = qemu_memalign(QHT_BUCKET_ALIGN, sizeof(*b));
+ memset(b, 0, sizeof(*b));
+ new = b;
+ atomic_inc(&map->n_added_buckets);
+ if (unlikely(qht_map_needs_resize(map)) && needs_resize) {
+ *needs_resize = true;
+ }
+ }
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i]) {
+ if (unlikely(b->pointers[i] == p)) {
+ return false;
+ }
+ continue;
+ }
+ /* found an empty key: acquire the seqlock and write */
+ seqlock_write_begin(&head->sequence);
+ if (new) {
+ /*
+ * This barrier is paired with smp_rmb() after reading
+ * b->next when not holding b->lock.
+ */
+ smp_wmb();
+ atomic_set(&prev->next, b);
+ }
+ atomic_set(&b->hashes[i], hash);
+ atomic_set(&b->pointers[i], p);
+ seqlock_write_end(&head->sequence);
+ return true;
+ }
+ prev = b;
+ b = b->next;
+ }
+}
+
+/* call with an external lock held */
+bool qht_insert(struct qht *ht, void *p, uint32_t hash)
+{
+ struct qht_map *map = ht->map;
+ struct qht_bucket *b = qht_map_to_bucket(map, hash);
+ bool needs_resize = false;
+ bool ret;
+
+ /* NULL pointers are not supported */
+ assert(p);
+
+ qemu_spin_lock(&b->lock);
+ ret = qht_insert__locked(ht, map, b, p, hash, &needs_resize);
+ qht_bucket_debug(b);
+ qemu_spin_unlock(&b->lock);
+
+ if (unlikely(needs_resize) && ht->mode & QHT_MODE_AUTO_RESIZE) {
+ qht_do_resize(ht, map->n * 2);
+ }
+ return ret;
+}
+
+static inline bool qht_entry_is_last(struct qht_bucket *b, int pos)
+{
+ if (pos == QHT_BUCKET_ENTRIES - 1) {
+ if (b->next == NULL) {
+ return true;
+ }
+ return b->next->pointers[0] == NULL;
+ }
+ return b->pointers[pos + 1] == NULL;
+}
+
+static void
+qht_entry_move(struct qht_bucket *to, int i, struct qht_bucket *from, int j)
+{
+ assert(!(to == from && i == j));
+ assert(to->pointers[i] == NULL);
+ assert(from->pointers[j]);
+
+ atomic_set(&to->hashes[i], from->hashes[j]);
+ atomic_set(&to->pointers[i], from->pointers[j]);
+
+ atomic_set(&from->hashes[j], 0);
+ atomic_set(&from->pointers[j], NULL);
+}
+
+/*
+ * Find the last valid entry in @head, and swap it with @orig[pos], which has
+ * just been invalidated.
+ */
+static inline void qht_bucket_fill_hole(struct qht_bucket *orig, int pos)
+{
+ struct qht_bucket *b = orig;
+ struct qht_bucket *prev = NULL;
+ int i;
+
+ if (qht_entry_is_last(orig, pos)) {
+ return;
+ }
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] || (b == orig && i == pos)) {
+ continue;
+ }
+ if (i > 0) {
+ return qht_entry_move(orig, pos, b, i - 1);
+ }
+ assert(prev);
+ return qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1);
+ }
+ prev = b;
+ b = b->next;
+ } while (b);
+ /* no free entries other than orig[pos], so swap it with the last one */
+ qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1);
+}
+
+/* call with b->lock held */
+static inline
+bool qht_remove__locked(struct qht_map *map, struct qht_bucket *head,
+ const void *p, uint32_t hash)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ void *q = b->pointers[i];
+
+ if (unlikely(q == NULL)) {
+ return false;
+ }
+ if (q == p) {
+ assert(b->hashes[i] == hash);
+ seqlock_write_begin(&head->sequence);
+ atomic_set(&b->hashes[i], 0);
+ atomic_set(&b->pointers[i], NULL);
+ qht_bucket_fill_hole(b, i);
+ seqlock_write_end(&head->sequence);
+ return true;
+ }
+ }
+ b = b->next;
+ } while (b);
+ return false;
+}
+
+/* call with an external lock held */
+bool qht_remove(struct qht *ht, const void *p, uint32_t hash)
+{
+ struct qht_map *map = ht->map;
+ struct qht_bucket *b = qht_map_to_bucket(map, hash);
+ bool ret;
+
+ qemu_spin_lock(&b->lock);
+ ret = qht_remove__locked(map, b, p, hash);
+ qht_bucket_debug(b);
+ qemu_spin_unlock(&b->lock);
+ return ret;
+}
+
+static inline void qht_bucket_iter(struct qht *ht, struct qht_bucket *b,
+ qht_iter_func_t func, void *userp)
+{
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ return;
+ }
+ func(ht, b->pointers[i], b->hashes[i], userp);
+ }
+ b = b->next;
+ } while (b);
+}
+
+/* external lock + all of the map's locks held */
+static inline void qht_map_iter__locked(struct qht *ht, struct qht_map *map,
+ qht_iter_func_t func, void *userp)
+{
+ size_t i;
+
+ for (i = 0; i < map->n; i++) {
+ qht_bucket_iter(ht, &map->buckets[i], func, userp);
+ }
+}
+
+/* call with an external lock held */
+void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp)
+{
+ qht_map_lock_buckets(ht->map);
+ qht_map_iter__locked(ht, ht->map, func, userp);
+ qht_map_unlock_buckets(ht->map);
+}
+
+static void qht_map_copy(struct qht *ht, void *p, uint32_t hash, void *userp)
+{
+ struct qht_map *new = userp;
+ struct qht_bucket *b = qht_map_to_bucket(new, hash);
+
+ /* no need to acquire b->lock because no thread has seen this map yet */
+ qht_insert__locked(ht, new, b, p, hash, NULL);
+}
+
+/* call with an external lock held */
+static void qht_do_resize(struct qht *ht, size_t n)
+{
+ struct qht_map *old = ht->map;
+ struct qht_map *new;
+
+ g_assert_cmpuint(n, !=, old->n);
+ new = qht_map_create(n);
+ qht_iter(ht, qht_map_copy, new);
+ qht_map_debug(new);
+
+ qht_publish(ht, new);
+ call_rcu1(&old->rcu, qht_map_reclaim);
+}
+
+/* call with an external lock held */
+bool qht_resize(struct qht *ht, size_t n_elems)
+{
+ size_t n = qht_elems_to_buckets(n_elems);
+
+ if (n == ht->map->n) {
+ return false;
+ }
+ qht_do_resize(ht, n);
+ return true;
+}
+
+/* pass @stats to qht_statistics_destroy() when done */
+void qht_statistics_init(struct qht *ht, struct qht_stats *stats)
+{
+ struct qht_map *map;
+ int i;
+
+ map = qht_map__atomic_mb(ht);
+
+ stats->head_buckets = map->n;
+ stats->used_head_buckets = 0;
+ stats->entries = 0;
+ qdist_init(&stats->chain);
+ qdist_init(&stats->occupancy);
+
+ for (i = 0; i < map->n; i++) {
+ struct qht_bucket *head = &map->buckets[i];
+ struct qht_bucket *b;
+ uint32_t version;
+ size_t buckets;
+ size_t entries;
+ int j;
+
+ do {
+ version = seqlock_read_begin(&head->sequence);
+ buckets = 0;
+ entries = 0;
+ b = head;
+ do {
+ for (j = 0; j < QHT_BUCKET_ENTRIES; j++) {
+ if (atomic_read(&b->pointers[j]) == NULL) {
+ break;
+ }
+ entries++;
+ }
+ buckets++;
+ b = bucket_next__atomic_mb(b);
+ } while (b);
+ } while (seqlock_read_retry(&head->sequence, version));
+
+ if (entries) {
+ qdist_inc(&stats->chain, buckets);
+ qdist_inc(&stats->occupancy,
+ (double)entries / QHT_BUCKET_ENTRIES / buckets);
+ stats->used_head_buckets++;
+ stats->entries += entries;
+ } else {
+ qdist_inc(&stats->occupancy, 0);
+ }
+ }
+}
+
+void qht_statistics_destroy(struct qht_stats *stats)
+{
+ qdist_destroy(&stats->occupancy);
+ qdist_destroy(&stats->chain);
+}
--
2.5.0
