The following commit has been merged into the locking/futex branch of tip: Commit-ID: e3924279e5164d821fa2cbcf0c15e7345cb3508e Gitweb: https://git.kernel.org/tip/e3924279e5164d821fa2cbcf0c15e7345cb3508e Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> AuthorDate: Wed, 26 Feb 2025 10:10:57 +01:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Wed, 26 Feb 2025 16:07:59 +01:00 futex: Use a hashmask instead of hashsize The global hash uses futex_hashsize to save the amount of the hash buckets that have been allocated during system boot. On each futex_hash() invocation this number is substracted by one to get the mask. This can be optimized by saving directly the mask avoiding the substraction on each futex_hash() invocation. Rename futex_hashsize to futex_hashmask and save the mask of the allocated hash map. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: Waiman Long <longman@xxxxxxxxxx> Link: https://lore.kernel.org/all/20250226091057.bX8vObR4@xxxxxxxxxxxxx --- kernel/futex/core.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index 3db8567..cca1585 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -50,10 +50,10 @@ */ static struct { struct futex_hash_bucket *queues; - unsigned long hashsize; + unsigned long hashmask; } __futex_data __read_mostly __aligned(2*sizeof(long)); #define futex_queues (__futex_data.queues) -#define futex_hashsize (__futex_data.hashsize) +#define futex_hashmask (__futex_data.hashmask) /* @@ -119,7 +119,7 @@ struct futex_hash_bucket *futex_hash(union futex_key *key) u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4, key->both.offset); - return &futex_queues[hash & (futex_hashsize - 1)]; + return &futex_queues[hash & futex_hashmask]; } @@ -1127,27 +1127,28 @@ void futex_exit_release(struct task_struct *tsk) static int __init futex_init(void) { + unsigned long hashsize, i; unsigned int futex_shift; - unsigned long i; #ifdef CONFIG_BASE_SMALL - futex_hashsize = 16; + hashsize = 16; #else - futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus()); + hashsize = roundup_pow_of_two(256 * num_possible_cpus()); #endif futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues), - futex_hashsize, 0, 0, + hashsize, 0, 0, &futex_shift, NULL, - futex_hashsize, futex_hashsize); - futex_hashsize = 1UL << futex_shift; + hashsize, hashsize); + hashsize = 1UL << futex_shift; - for (i = 0; i < futex_hashsize; i++) { + for (i = 0; i < hashsize; i++) { atomic_set(&futex_queues[i].waiters, 0); plist_head_init(&futex_queues[i].chain); spin_lock_init(&futex_queues[i].lock); } + futex_hashmask = hashsize - 1; return 0; } core_initcall(futex_init);
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