From d0c006402e7941558e5283ae434e2847c7999378 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Wed, 19 Oct 2022 16:08:50 +0200 Subject: jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked() Use atomic_try_cmpxchg() instead of atomic_cmpxchg (*ptr, old, new) == old in static_key_slow_inc_cpuslocked(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@gmail.com --- kernel/jump_label.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'kernel') diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 714ac4c3b556..4d6c6f5f60db 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -115,8 +115,6 @@ EXPORT_SYMBOL_GPL(static_key_count); void static_key_slow_inc_cpuslocked(struct static_key *key) { - int v, v1; - STATIC_KEY_CHECK_USE(key); lockdep_assert_cpus_held(); @@ -132,11 +130,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) * so it counts as "enabled" in jump_label_update(). Note that * atomic_inc_unless_negative() checks >= 0, so roll our own. */ - for (v = atomic_read(&key->enabled); v > 0; v = v1) { - v1 = atomic_cmpxchg(&key->enabled, v, v + 1); - if (likely(v1 == v)) + for (int v = atomic_read(&key->enabled); v > 0; ) + if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))) return; - } jump_label_lock(); if (atomic_read(&key->enabled) == 0) { -- cgit v1.2.3-58-ga151