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Per object mutexes may come with significant memory cost while a
global mutex can suffer from unnecessary contention. A sharded mutex
is a compromise where objects are hashed and then a particular mutex
for the hash of the object used. Contention can be controlled by the
number of shards.
v2. Use hashmap.h's hash_bits in case of contention from alignment of
objects.
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andres Freund <andres@anarazel.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Yuan Can <yuancan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/r/20230615040715.2064350-1-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
30 lines
922 B
C
30 lines
922 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef PERF_SHARDED_MUTEX_H
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#define PERF_SHARDED_MUTEX_H
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#include "mutex.h"
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#include "hashmap.h"
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/*
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* In a situation where a lock is needed per object, having a mutex can be
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* relatively memory expensive (40 bytes on x86-64). If the object can be
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* constantly hashed, a sharded mutex is an alternative global pool of mutexes
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* where the mutex is looked up from a hash value. This can lead to collisions
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* if the number of shards isn't large enough.
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*/
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struct sharded_mutex {
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/* mutexes array is 1<<cap_bits in size. */
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unsigned int cap_bits;
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struct mutex mutexes[];
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};
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struct sharded_mutex *sharded_mutex__new(size_t num_shards);
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void sharded_mutex__delete(struct sharded_mutex *sm);
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static inline struct mutex *sharded_mutex__get_mutex(struct sharded_mutex *sm, size_t hash)
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{
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return &sm->mutexes[hash_bits(hash, sm->cap_bits)];
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}
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#endif /* PERF_SHARDED_MUTEX_H */
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