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A single update for futexes:

Browse Source 
Use a precomputed mask for the hash computation instead of computing the
   mask from the size on every invocation.
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Merge tag 'locking-futex-2025-03-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull futex update from Thomas Gleixner:
 "A single update for futexes:

  Use a precomputed mask for the hash computation instead of computing
  the mask from the size on every invocation"

* tag 'locking-futex-2025-03-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Use a hashmask instead of hashsize
This commit is contained in:
Linus Torvalds 2025-03-25 10:00:17 -07:00
commit 0ae2062ee3
1 changed files with 11 additions and 10 deletions
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21
kernel/futex/core.c
View File

@ -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);