Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] jump_label: use atomic_try_cmpxchg in static_key_slow_inc_cpuslocked | Date | Wed, 19 Oct 2022 16:08:50 +0200 |
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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.
Cc: Peter Zijlstra <peterz@infradead.org> Cc: Josh Poimboeuf <jpoimboe@kernel.org> Cc: Jason Baron <jbaron@akamai.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- kernel/jump_label.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
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) { -- 2.37.3
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