Commit e3924279 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Thomas Gleixner
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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: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
Link: https://lore.kernel.org/all/20250226091057.bX8vObR4@linutronix.de
parent d082ecbc

kernel/futex/core.c

+11 −10
Original line number Diff line number Diff line
@@ -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);