The following commit has been merged into the locking/core branch of tip:
Commit-ID: d0c006402e7941558e5283ae434e2847c7999378
Gitweb: https://git.kernel.org/tip/d0c006402e7941558e5283ae434e2847c7999378
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Wed, 19 Oct 2022 16:08:50 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 27 Oct 2022 10:35:41 +02:00
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 <ubizjak@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@xxxxxxxxx
---
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 714ac4c..4d6c6f5 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) {
|