linux-kernel - [GIT pull] locking/futex for v6.15-rc1

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Message-ID: <174275226072.1561082.5650620916174411892.tglx@xen13>
Date: Sun, 23 Mar 2025 18:51:38 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [GIT pull] locking/futex for v6.15-rc1

Linus,

please pull the latest locking/futex branch from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git locking-futex-2025-03-23

up to:  e3924279e516: futex: Use a hashmask instead of hashsize


A single update for futexes:

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


Thanks,

	tglx

------------------>
Sebastian Andrzej Siewior (1):
      futex: Use a hashmask instead of hashsize


 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 3db8567f5a44..cca15859a50b 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);