1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef PERF_SHARDED_MUTEX_H
3#define PERF_SHARDED_MUTEX_H
4
5#include "mutex.h"
6#include "hashmap.h"
7
8/*
9 * In a situation where a lock is needed per object, having a mutex can be
10 * relatively memory expensive (40 bytes on x86-64). If the object can be
11 * constantly hashed, a sharded mutex is an alternative global pool of mutexes
12 * where the mutex is looked up from a hash value. This can lead to collisions
13 * if the number of shards isn't large enough.
14 */
15struct sharded_mutex {
16	/* mutexes array is 1<<cap_bits in size. */
17	unsigned int cap_bits;
18	struct mutex mutexes[];
19};
20
21struct sharded_mutex *sharded_mutex__new(size_t num_shards);
22void sharded_mutex__delete(struct sharded_mutex *sm);
23
24static inline struct mutex *sharded_mutex__get_mutex(struct sharded_mutex *sm, size_t hash)
25{
26	return &sm->mutexes[hash_bits(hash, sm->cap_bits)];
27}
28
29#endif  /* PERF_SHARDED_MUTEX_H */
30