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