Re: [RFC][PATCH] Scalable Scheduling

[Linus Torvalds]

On Wed, 8 Aug 2001, Daniel Phillips wrote:
>
> write:
>
> 	inline int nr_running(void)
> 	{
> 	#ifdef CONFIG_SMP
> 		int i = 0, tot=nt_running(REALTIME_RQ);
> 		while (i < smp_num_cpus) {
> 			tot += nt_running(cpu_logical_map(i++));
> 		}
> 		return(tot);
> 	#else
> 		return nr_running;
> 	#endif
> 	}

Even more preferably, just have (in a header file)

	#ifdef CONFIG_SMP

	inline int nr_running(void)
	{
		...
	}

	.. other SMP cases ..

	#else

	#define nr_running() (__nr_running)

	.. other UP cases ..

	#endif

if you just cannot make an efficient function that just works for both.

No, we don't adhere to this everywhere. But we should (and largely _do_)
try to.

Having the #ifdef's outside the code tends to have two advantages:

 - it makes the code much more readable, and doesn't split things up.

 - you have to choose your abstraction interfaces more carefully, which in
   turn tends to make for better code.

Abstraction is nice - _especially_ when you have a compiler that sees
through the abstraction and can generate code as if it wasn't there.

		Linus