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);
|