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. Signed-off-by: Emilio G. Cota <cota@braap.org> Message-Id: <1465412133-3029-11-git-send-email-cota@braap.org> Signed-off-by: Richard Henderson <rth@twiddle.net>
834 lines
23 KiB
C
834 lines
23 KiB
C
/*
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* qht.c - QEMU Hash Table, designed to scale for read-mostly workloads.
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*
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* Copyright (C) 2016, Emilio G. Cota <cota@braap.org>
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*
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* License: GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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* Assumptions:
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* - NULL cannot be inserted/removed as a pointer value.
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* - Trying to insert an already-existing hash-pointer pair is OK. However,
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* it is not OK to insert into the same hash table different hash-pointer
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* pairs that have the same pointer value, but not the hashes.
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* - Lookups are performed under an RCU read-critical section; removals
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* must wait for a grace period to elapse before freeing removed objects.
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*
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* Features:
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* - Reads (i.e. lookups and iterators) can be concurrent with other reads.
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* Lookups that are concurrent with writes to the same bucket will retry
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* via a seqlock; iterators acquire all bucket locks and therefore can be
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* concurrent with lookups and are serialized wrt writers.
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* - Writes (i.e. insertions/removals) can be concurrent with writes to
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* different buckets; writes to the same bucket are serialized through a lock.
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* - Optional auto-resizing: the hash table resizes up if the load surpasses
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* a certain threshold. Resizing is done concurrently with readers; writes
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* are serialized with the resize operation.
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*
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* The key structure is the bucket, which is cacheline-sized. Buckets
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* contain a few hash values and pointers; the u32 hash values are stored in
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* full so that resizing is fast. Having this structure instead of directly
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* chaining items has two advantages:
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* - Failed lookups fail fast, and touch a minimum number of cache lines.
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* - Resizing the hash table with concurrent lookups is easy.
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*
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* There are two types of buckets:
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* 1. "head" buckets are the ones allocated in the array of buckets in qht_map.
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* 2. all "non-head" buckets (i.e. all others) are members of a chain that
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* starts from a head bucket.
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* Note that the seqlock and spinlock of a head bucket applies to all buckets
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* chained to it; these two fields are unused in non-head buckets.
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*
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* On removals, we move the last valid item in the chain to the position of the
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* just-removed entry. This makes lookups slightly faster, since the moment an
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* invalid entry is found, the (failed) lookup is over.
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*
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* Resizing is done by taking all bucket spinlocks (so that no other writers can
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* race with us) and then copying all entries into a new hash map. Then, the
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* ht->map pointer is set, and the old map is freed once no RCU readers can see
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* it anymore.
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*
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* Writers check for concurrent resizes by comparing ht->map before and after
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* acquiring their bucket lock. If they don't match, a resize has occured
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* while the bucket spinlock was being acquired.
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*
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* Related Work:
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* - Idea of cacheline-sized buckets with full hashes taken from:
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* David, Guerraoui & Trigonakis, "Asynchronized Concurrency:
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* The Secret to Scaling Concurrent Search Data Structures", ASPLOS'15.
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* - Why not RCU-based hash tables? They would allow us to get rid of the
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* seqlock, but resizing would take forever since RCU read critical
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* sections in QEMU take quite a long time.
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* More info on relativistic hash tables:
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* + Triplett, McKenney & Walpole, "Resizable, Scalable, Concurrent Hash
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* Tables via Relativistic Programming", USENIX ATC'11.
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* + Corbet, "Relativistic hash tables, part 1: Algorithms", @ lwn.net, 2014.
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* https://lwn.net/Articles/612021/
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*/
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#include "qemu/qht.h"
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#include "qemu/atomic.h"
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#include "qemu/rcu.h"
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//#define QHT_DEBUG
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/*
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* We want to avoid false sharing of cache lines. Most systems have 64-byte
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* cache lines so we go with it for simplicity.
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*
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* Note that systems with smaller cache lines will be fine (the struct is
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* almost 64-bytes); systems with larger cache lines might suffer from
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* some false sharing.
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*/
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#define QHT_BUCKET_ALIGN 64
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/* define these to keep sizeof(qht_bucket) within QHT_BUCKET_ALIGN */
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#if HOST_LONG_BITS == 32
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#define QHT_BUCKET_ENTRIES 6
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#else /* 64-bit */
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#define QHT_BUCKET_ENTRIES 4
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#endif
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/*
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* Note: reading partially-updated pointers in @pointers could lead to
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* segfaults. We thus access them with atomic_read/set; this guarantees
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* that the compiler makes all those accesses atomic. We also need the
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* volatile-like behavior in atomic_read, since otherwise the compiler
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* might refetch the pointer.
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* atomic_read's are of course not necessary when the bucket lock is held.
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*
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* If both ht->lock and b->lock are grabbed, ht->lock should always
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* be grabbed first.
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*/
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struct qht_bucket {
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QemuSpin lock;
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QemuSeqLock sequence;
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uint32_t hashes[QHT_BUCKET_ENTRIES];
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void *pointers[QHT_BUCKET_ENTRIES];
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struct qht_bucket *next;
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} QEMU_ALIGNED(QHT_BUCKET_ALIGN);
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QEMU_BUILD_BUG_ON(sizeof(struct qht_bucket) > QHT_BUCKET_ALIGN);
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/**
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* struct qht_map - structure to track an array of buckets
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* @rcu: used by RCU. Keep it as the top field in the struct to help valgrind
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* find the whole struct.
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* @buckets: array of head buckets. It is constant once the map is created.
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* @n_buckets: number of head buckets. It is constant once the map is created.
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* @n_added_buckets: number of added (i.e. "non-head") buckets
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* @n_added_buckets_threshold: threshold to trigger an upward resize once the
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* number of added buckets surpasses it.
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*
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* Buckets are tracked in what we call a "map", i.e. this structure.
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*/
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struct qht_map {
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struct rcu_head rcu;
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struct qht_bucket *buckets;
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size_t n_buckets;
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size_t n_added_buckets;
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size_t n_added_buckets_threshold;
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};
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/* trigger a resize when n_added_buckets > n_buckets / div */
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#define QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV 8
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static void qht_do_resize(struct qht *ht, struct qht_map *new);
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static void qht_grow_maybe(struct qht *ht);
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#ifdef QHT_DEBUG
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#define qht_debug_assert(X) do { assert(X); } while (0)
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static void qht_bucket_debug__locked(struct qht_bucket *b)
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{
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bool seen_empty = false;
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bool corrupt = false;
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int i;
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do {
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for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
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if (b->pointers[i] == NULL) {
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seen_empty = true;
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continue;
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}
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if (seen_empty) {
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fprintf(stderr, "%s: b: %p, pos: %i, hash: 0x%x, p: %p\n",
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__func__, b, i, b->hashes[i], b->pointers[i]);
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corrupt = true;
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}
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}
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b = b->next;
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} while (b);
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qht_debug_assert(!corrupt);
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}
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static void qht_map_debug__all_locked(struct qht_map *map)
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{
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int i;
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for (i = 0; i < map->n_buckets; i++) {
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qht_bucket_debug__locked(&map->buckets[i]);
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}
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}
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#else
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#define qht_debug_assert(X) do { (void)(X); } while (0)
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static inline void qht_bucket_debug__locked(struct qht_bucket *b)
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{ }
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static inline void qht_map_debug__all_locked(struct qht_map *map)
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{ }
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#endif /* QHT_DEBUG */
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static inline size_t qht_elems_to_buckets(size_t n_elems)
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{
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return pow2ceil(n_elems / QHT_BUCKET_ENTRIES);
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}
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static inline void qht_head_init(struct qht_bucket *b)
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{
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memset(b, 0, sizeof(*b));
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qemu_spin_init(&b->lock);
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seqlock_init(&b->sequence);
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}
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static inline
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struct qht_bucket *qht_map_to_bucket(struct qht_map *map, uint32_t hash)
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{
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return &map->buckets[hash & (map->n_buckets - 1)];
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}
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/* acquire all bucket locks from a map */
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static void qht_map_lock_buckets(struct qht_map *map)
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{
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size_t i;
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for (i = 0; i < map->n_buckets; i++) {
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struct qht_bucket *b = &map->buckets[i];
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qemu_spin_lock(&b->lock);
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}
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}
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static void qht_map_unlock_buckets(struct qht_map *map)
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{
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size_t i;
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for (i = 0; i < map->n_buckets; i++) {
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struct qht_bucket *b = &map->buckets[i];
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qemu_spin_unlock(&b->lock);
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}
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}
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/*
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* Call with at least a bucket lock held.
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* @map should be the value read before acquiring the lock (or locks).
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*/
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static inline bool qht_map_is_stale__locked(struct qht *ht, struct qht_map *map)
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{
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return map != ht->map;
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}
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/*
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* Grab all bucket locks, and set @pmap after making sure the map isn't stale.
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*
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* Pairs with qht_map_unlock_buckets(), hence the pass-by-reference.
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*
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* Note: callers cannot have ht->lock held.
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*/
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static inline
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void qht_map_lock_buckets__no_stale(struct qht *ht, struct qht_map **pmap)
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{
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struct qht_map *map;
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map = atomic_rcu_read(&ht->map);
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qht_map_lock_buckets(map);
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if (likely(!qht_map_is_stale__locked(ht, map))) {
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*pmap = map;
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return;
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}
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qht_map_unlock_buckets(map);
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/* we raced with a resize; acquire ht->lock to see the updated ht->map */
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qemu_mutex_lock(&ht->lock);
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map = ht->map;
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qht_map_lock_buckets(map);
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qemu_mutex_unlock(&ht->lock);
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*pmap = map;
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return;
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}
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/*
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* Get a head bucket and lock it, making sure its parent map is not stale.
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* @pmap is filled with a pointer to the bucket's parent map.
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*
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* Unlock with qemu_spin_unlock(&b->lock).
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*
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* Note: callers cannot have ht->lock held.
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*/
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static inline
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struct qht_bucket *qht_bucket_lock__no_stale(struct qht *ht, uint32_t hash,
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struct qht_map **pmap)
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{
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struct qht_bucket *b;
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struct qht_map *map;
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map = atomic_rcu_read(&ht->map);
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b = qht_map_to_bucket(map, hash);
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qemu_spin_lock(&b->lock);
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if (likely(!qht_map_is_stale__locked(ht, map))) {
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*pmap = map;
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return b;
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}
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qemu_spin_unlock(&b->lock);
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/* we raced with a resize; acquire ht->lock to see the updated ht->map */
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qemu_mutex_lock(&ht->lock);
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map = ht->map;
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b = qht_map_to_bucket(map, hash);
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qemu_spin_lock(&b->lock);
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qemu_mutex_unlock(&ht->lock);
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*pmap = map;
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return b;
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}
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static inline bool qht_map_needs_resize(struct qht_map *map)
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{
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return atomic_read(&map->n_added_buckets) > map->n_added_buckets_threshold;
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}
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static inline void qht_chain_destroy(struct qht_bucket *head)
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{
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struct qht_bucket *curr = head->next;
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struct qht_bucket *prev;
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while (curr) {
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prev = curr;
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curr = curr->next;
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qemu_vfree(prev);
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}
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}
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/* pass only an orphan map */
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static void qht_map_destroy(struct qht_map *map)
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{
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size_t i;
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for (i = 0; i < map->n_buckets; i++) {
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qht_chain_destroy(&map->buckets[i]);
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}
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qemu_vfree(map->buckets);
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g_free(map);
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}
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static struct qht_map *qht_map_create(size_t n_buckets)
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{
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struct qht_map *map;
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size_t i;
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map = g_malloc(sizeof(*map));
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map->n_buckets = n_buckets;
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map->n_added_buckets = 0;
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map->n_added_buckets_threshold = n_buckets /
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QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV;
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/* let tiny hash tables to at least add one non-head bucket */
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if (unlikely(map->n_added_buckets_threshold == 0)) {
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map->n_added_buckets_threshold = 1;
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}
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map->buckets = qemu_memalign(QHT_BUCKET_ALIGN,
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sizeof(*map->buckets) * n_buckets);
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for (i = 0; i < n_buckets; i++) {
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qht_head_init(&map->buckets[i]);
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}
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return map;
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}
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void qht_init(struct qht *ht, size_t n_elems, unsigned int mode)
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{
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struct qht_map *map;
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size_t n_buckets = qht_elems_to_buckets(n_elems);
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ht->mode = mode;
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qemu_mutex_init(&ht->lock);
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map = qht_map_create(n_buckets);
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atomic_rcu_set(&ht->map, map);
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}
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/* call only when there are no readers/writers left */
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void qht_destroy(struct qht *ht)
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{
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qht_map_destroy(ht->map);
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memset(ht, 0, sizeof(*ht));
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}
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static void qht_bucket_reset__locked(struct qht_bucket *head)
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{
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struct qht_bucket *b = head;
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int i;
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seqlock_write_begin(&head->sequence);
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do {
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for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
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if (b->pointers[i] == NULL) {
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goto done;
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}
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b->hashes[i] = 0;
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atomic_set(&b->pointers[i], NULL);
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}
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b = b->next;
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} while (b);
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done:
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seqlock_write_end(&head->sequence);
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}
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/* call with all bucket locks held */
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static void qht_map_reset__all_locked(struct qht_map *map)
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{
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size_t i;
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for (i = 0; i < map->n_buckets; i++) {
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qht_bucket_reset__locked(&map->buckets[i]);
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}
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qht_map_debug__all_locked(map);
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}
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void qht_reset(struct qht *ht)
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{
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struct qht_map *map;
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qht_map_lock_buckets__no_stale(ht, &map);
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qht_map_reset__all_locked(map);
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qht_map_unlock_buckets(map);
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}
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bool qht_reset_size(struct qht *ht, size_t n_elems)
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{
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struct qht_map *new;
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struct qht_map *map;
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size_t n_buckets;
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bool resize = false;
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n_buckets = qht_elems_to_buckets(n_elems);
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qemu_mutex_lock(&ht->lock);
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map = ht->map;
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if (n_buckets != map->n_buckets) {
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new = qht_map_create(n_buckets);
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resize = true;
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}
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qht_map_lock_buckets(map);
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qht_map_reset__all_locked(map);
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if (resize) {
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qht_do_resize(ht, new);
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}
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qht_map_unlock_buckets(map);
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qemu_mutex_unlock(&ht->lock);
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return resize;
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}
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static inline
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void *qht_do_lookup(struct qht_bucket *head, qht_lookup_func_t func,
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const void *userp, uint32_t hash)
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{
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struct qht_bucket *b = head;
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int i;
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do {
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for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
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if (b->hashes[i] == hash) {
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void *p = atomic_read(&b->pointers[i]);
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if (likely(p) && likely(func(p, userp))) {
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return p;
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}
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}
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}
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b = atomic_rcu_read(&b->next);
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} while (b);
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return NULL;
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}
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static __attribute__((noinline))
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void *qht_lookup__slowpath(struct qht_bucket *b, qht_lookup_func_t func,
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const void *userp, uint32_t hash)
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{
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unsigned int version;
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void *ret;
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do {
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version = seqlock_read_begin(&b->sequence);
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ret = qht_do_lookup(b, func, userp, hash);
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} while (seqlock_read_retry(&b->sequence, version));
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return ret;
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}
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void *qht_lookup(struct qht *ht, qht_lookup_func_t func, const void *userp,
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uint32_t hash)
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{
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struct qht_bucket *b;
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struct qht_map *map;
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unsigned int version;
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void *ret;
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map = atomic_rcu_read(&ht->map);
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b = qht_map_to_bucket(map, hash);
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version = seqlock_read_begin(&b->sequence);
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ret = qht_do_lookup(b, func, userp, hash);
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if (likely(!seqlock_read_retry(&b->sequence, version))) {
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return ret;
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|
}
|
|
/*
|
|
* 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;
|
|
|
|
do {
|
|
for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
|
|
if (b->pointers[i]) {
|
|
if (unlikely(b->pointers[i] == p)) {
|
|
return false;
|
|
}
|
|
} else {
|
|
goto found;
|
|
}
|
|
}
|
|
prev = b;
|
|
b = b->next;
|
|
} while (b);
|
|
|
|
b = qemu_memalign(QHT_BUCKET_ALIGN, sizeof(*b));
|
|
memset(b, 0, sizeof(*b));
|
|
new = b;
|
|
i = 0;
|
|
atomic_inc(&map->n_added_buckets);
|
|
if (unlikely(qht_map_needs_resize(map)) && needs_resize) {
|
|
*needs_resize = true;
|
|
}
|
|
|
|
found:
|
|
/* found an empty key: acquire the seqlock and write */
|
|
seqlock_write_begin(&head->sequence);
|
|
if (new) {
|
|
atomic_rcu_set(&prev->next, b);
|
|
}
|
|
b->hashes[i] = hash;
|
|
atomic_set(&b->pointers[i], p);
|
|
seqlock_write_end(&head->sequence);
|
|
return true;
|
|
}
|
|
|
|
static __attribute__((noinline)) void qht_grow_maybe(struct qht *ht)
|
|
{
|
|
struct qht_map *map;
|
|
|
|
/*
|
|
* If the lock is taken it probably means there's an ongoing resize,
|
|
* so bail out.
|
|
*/
|
|
if (qemu_mutex_trylock(&ht->lock)) {
|
|
return;
|
|
}
|
|
map = ht->map;
|
|
/* another thread might have just performed the resize we were after */
|
|
if (qht_map_needs_resize(map)) {
|
|
struct qht_map *new = qht_map_create(map->n_buckets * 2);
|
|
|
|
qht_map_lock_buckets(map);
|
|
qht_do_resize(ht, new);
|
|
qht_map_unlock_buckets(map);
|
|
}
|
|
qemu_mutex_unlock(&ht->lock);
|
|
}
|
|
|
|
bool qht_insert(struct qht *ht, void *p, uint32_t hash)
|
|
{
|
|
struct qht_bucket *b;
|
|
struct qht_map *map;
|
|
bool needs_resize = false;
|
|
bool ret;
|
|
|
|
/* NULL pointers are not supported */
|
|
qht_debug_assert(p);
|
|
|
|
b = qht_bucket_lock__no_stale(ht, hash, &map);
|
|
ret = qht_insert__locked(ht, map, b, p, hash, &needs_resize);
|
|
qht_bucket_debug__locked(b);
|
|
qemu_spin_unlock(&b->lock);
|
|
|
|
if (unlikely(needs_resize) && ht->mode & QHT_MODE_AUTO_RESIZE) {
|
|
qht_grow_maybe(ht);
|
|
}
|
|
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)
|
|
{
|
|
qht_debug_assert(!(to == from && i == j));
|
|
qht_debug_assert(to->pointers[i]);
|
|
qht_debug_assert(from->pointers[j]);
|
|
|
|
to->hashes[i] = from->hashes[j];
|
|
atomic_set(&to->pointers[i], from->pointers[j]);
|
|
|
|
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_remove_entry(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)) {
|
|
orig->hashes[pos] = 0;
|
|
atomic_set(&orig->pointers[pos], NULL);
|
|
return;
|
|
}
|
|
do {
|
|
for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
|
|
if (b->pointers[i]) {
|
|
continue;
|
|
}
|
|
if (i > 0) {
|
|
return qht_entry_move(orig, pos, b, i - 1);
|
|
}
|
|
qht_debug_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) {
|
|
qht_debug_assert(b->hashes[i] == hash);
|
|
seqlock_write_begin(&head->sequence);
|
|
qht_bucket_remove_entry(b, i);
|
|
seqlock_write_end(&head->sequence);
|
|
return true;
|
|
}
|
|
}
|
|
b = b->next;
|
|
} while (b);
|
|
return false;
|
|
}
|
|
|
|
bool qht_remove(struct qht *ht, const void *p, uint32_t hash)
|
|
{
|
|
struct qht_bucket *b;
|
|
struct qht_map *map;
|
|
bool ret;
|
|
|
|
/* NULL pointers are not supported */
|
|
qht_debug_assert(p);
|
|
|
|
b = qht_bucket_lock__no_stale(ht, hash, &map);
|
|
ret = qht_remove__locked(map, b, p, hash);
|
|
qht_bucket_debug__locked(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);
|
|
}
|
|
|
|
/* call with all of the map's locks held */
|
|
static inline void qht_map_iter__all_locked(struct qht *ht, struct qht_map *map,
|
|
qht_iter_func_t func, void *userp)
|
|
{
|
|
size_t i;
|
|
|
|
for (i = 0; i < map->n_buckets; i++) {
|
|
qht_bucket_iter(ht, &map->buckets[i], func, userp);
|
|
}
|
|
}
|
|
|
|
void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp)
|
|
{
|
|
struct qht_map *map;
|
|
|
|
map = atomic_rcu_read(&ht->map);
|
|
qht_map_lock_buckets(map);
|
|
/* Note: ht here is merely for carrying ht->mode; ht->map won't be read */
|
|
qht_map_iter__all_locked(ht, map, func, userp);
|
|
qht_map_unlock_buckets(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 ht->lock and all bucket locks held.
|
|
*
|
|
* Creating the @new map here would add unnecessary delay while all the locks
|
|
* are held--holding up the bucket locks is particularly bad, since no writes
|
|
* can occur while these are held. Thus, we let callers create the new map,
|
|
* hopefully without the bucket locks held.
|
|
*/
|
|
static void qht_do_resize(struct qht *ht, struct qht_map *new)
|
|
{
|
|
struct qht_map *old;
|
|
|
|
old = ht->map;
|
|
g_assert_cmpuint(new->n_buckets, !=, old->n_buckets);
|
|
|
|
qht_map_iter__all_locked(ht, old, qht_map_copy, new);
|
|
qht_map_debug__all_locked(new);
|
|
|
|
atomic_rcu_set(&ht->map, new);
|
|
call_rcu(old, qht_map_destroy, rcu);
|
|
}
|
|
|
|
bool qht_resize(struct qht *ht, size_t n_elems)
|
|
{
|
|
size_t n_buckets = qht_elems_to_buckets(n_elems);
|
|
size_t ret = false;
|
|
|
|
qemu_mutex_lock(&ht->lock);
|
|
if (n_buckets != ht->map->n_buckets) {
|
|
struct qht_map *new;
|
|
struct qht_map *old = ht->map;
|
|
|
|
new = qht_map_create(n_buckets);
|
|
qht_map_lock_buckets(old);
|
|
qht_do_resize(ht, new);
|
|
qht_map_unlock_buckets(old);
|
|
ret = true;
|
|
}
|
|
qemu_mutex_unlock(&ht->lock);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/* 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 = atomic_rcu_read(&ht->map);
|
|
|
|
stats->head_buckets = map->n_buckets;
|
|
stats->used_head_buckets = 0;
|
|
stats->entries = 0;
|
|
qdist_init(&stats->chain);
|
|
qdist_init(&stats->occupancy);
|
|
|
|
for (i = 0; i < map->n_buckets; i++) {
|
|
struct qht_bucket *head = &map->buckets[i];
|
|
struct qht_bucket *b;
|
|
unsigned int 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 = atomic_rcu_read(&b->next);
|
|
} 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);
|
|
}
|