1 /* SPDX-License-Identifier: GPL-2.0 */ 1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef PERF_SHARDED_MUTEX_H 2 #ifndef PERF_SHARDED_MUTEX_H
3 #define PERF_SHARDED_MUTEX_H 3 #define PERF_SHARDED_MUTEX_H
4 4
5 #include "mutex.h" 5 #include "mutex.h"
6 #include "hashmap.h" 6 #include "hashmap.h"
7 7
8 /* 8 /*
9 * In a situation where a lock is needed per o 9 * In a situation where a lock is needed per object, having a mutex can be
10 * relatively memory expensive (40 bytes on x8 10 * relatively memory expensive (40 bytes on x86-64). If the object can be
11 * constantly hashed, a sharded mutex is an al 11 * constantly hashed, a sharded mutex is an alternative global pool of mutexes
12 * where the mutex is looked up from a hash va 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. 13 * if the number of shards isn't large enough.
14 */ 14 */
15 struct sharded_mutex { 15 struct sharded_mutex {
16 /* mutexes array is 1<<cap_bits in siz 16 /* mutexes array is 1<<cap_bits in size. */
17 unsigned int cap_bits; 17 unsigned int cap_bits;
18 struct mutex mutexes[]; 18 struct mutex mutexes[];
19 }; 19 };
20 20
21 struct sharded_mutex *sharded_mutex__new(size_ 21 struct sharded_mutex *sharded_mutex__new(size_t num_shards);
22 void sharded_mutex__delete(struct sharded_mute 22 void sharded_mutex__delete(struct sharded_mutex *sm);
23 23
24 static inline struct mutex *sharded_mutex__get 24 static inline struct mutex *sharded_mutex__get_mutex(struct sharded_mutex *sm, size_t hash)
25 { 25 {
26 return &sm->mutexes[hash_bits(hash, sm 26 return &sm->mutexes[hash_bits(hash, sm->cap_bits)];
27 } 27 }
28 28
29 #endif /* PERF_SHARDED_MUTEX_H */ 29 #endif /* PERF_SHARDED_MUTEX_H */
30 30
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