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 */
15 struct sharded_mutex {
16 /* mutexes array is 1<<cap_bits in size. */
17 unsigned int cap_bits;
18 struct mutex mutexes[];
19 };
20
21 struct sharded_mutex *sharded_mutex__new(size_t num_shards);
22 void sharded_mutex__delete(struct sharded_mutex *sm);
23
24 static 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
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