Re: [PATCH] locking/lock_events: Use this_cpu_add() when necessary

[Linus Torvalds]

On Wed, May 22, 2019 at 8:40 AM Waiman Long <longman@xxxxxxxxxx> wrote:
>
> +#if defined(CONFIG_PREEMPT) && \
> +   (defined(CONFIG_DEBUG_PREEMPT) || !defined(CONFIG_X86))
> +#define lockevent_percpu_inc(x)                this_cpu_inc(x)
> +#define lockevent_percpu_add(x, v)     this_cpu_add(x, v)

Why that CONFIG_X86 special case?

On x86, the regular non-underscore versionm is perfectly fine, and the
underscore is no faster or simpler.

So just make it be

   #if defined(CONFIG_PREEMPT)
     .. non-underscore versions..
   #else
     .. underscore versions ..
   #endif

and realize that x86 simply doesn't _care_. On x86, it will be one
single instruction regardless.

Non-x86 may prefer the underscore versions for the non-preempt case.

             Linus