Re: [PATCH REPOST] locking/local_lock: Make the empty local_lock_*() function a macro.

[Davidlohr Bueso]

On Tue, 08 Feb 2022, Sebastian Andrzej Siewior wrote:

> 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@xxxxxxxxxxxxx>
> Reviewed-by: Waiman Long <longman@xxxxxxxxxx>

Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>