linux-kernel - [tip: locking/core] locking/local_lock: Make the empty local_lock

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Message-ID: <164457821956.16921.6260017427574423665.tip-bot2@tip-bot2>
Date:   Fri, 11 Feb 2022 11:16:59 -0000
From:   "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Waiman Long <longman@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/local_lock: Make the empty local_lock_*()
 function a macro.

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     9983a9d577db415c41099a20a5637ab25dd3c240
Gitweb:        https://git.kernel.org/tip/9983a9d577db415c41099a20a5637ab25dd3c240
Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate:    Tue, 08 Feb 2022 18:08:02 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 11 Feb 2022 12:13:56 +01:00

locking/local_lock: Make the empty local_lock_*() function a macro.

It has been said that local_lock() does not add any overhead compared to
preempt_disable() in a !LOCKDEP configuration. A micro benchmark showed
an unexpected result which can be reduced to the fact that local_lock()
was not entirely optimized away.
In the !LOCKDEP configuration local_lock_acquire() is an empty static
inline function. On x86 the this_cpu_ptr() argument of that function is
fully evaluated leading to an additional mov+add instructions which are
not needed and not used.

Replace the static inline function with a macro. The typecheck() macro
ensures that the argument is of proper type while the resulting
disassembly shows no traces of this_cpu_ptr().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Waiman Long <longman@...hat.com>
Link: https://lkml.kernel.org/r/YgKjciR60fZft2l4@linutronix.de
---
 include/linux/local_lock_internal.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
index 975e33b..6d635e8 100644
--- a/include/linux/local_lock_internal.h
+++ b/include/linux/local_lock_internal.h
@@ -44,9 +44,9 @@ static inline void local_lock_debug_init(local_lock_t *l)
 }
 #else /* CONFIG_DEBUG_LOCK_ALLOC */
 # define LOCAL_LOCK_DEBUG_INIT(lockname)
-static inline void local_lock_acquire(local_lock_t *l) { }
-static inline void local_lock_release(local_lock_t *l) { }
-static inline void local_lock_debug_init(local_lock_t *l) { }
+# define local_lock_acquire(__ll)  do { typecheck(local_lock_t *, __ll); } while (0)
+# define local_lock_release(__ll)  do { typecheck(local_lock_t *, __ll); } while (0)
+# define local_lock_debug_init(__ll)  do { typecheck(local_lock_t *, __ll); } while (0)
 #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 
 #define INIT_LOCAL_LOCK(lockname)	{ LOCAL_LOCK_DEBUG_INIT(lockname) }