Re: [PATCH 2/4]: CPUIDLE: Introduce architecture independent cpuidle_pm_idle in drivers/cpuidle/cpuidle.c

On Thu, 2009-08-27 at 14:53 +0200, Peter Zijlstra wrote:

I'm not quite seeing how this makes anything any better. Not we have 3
function pointers, where 1 should suffice.

There's also the question of us having different "idle" vs.
"power_save", the former being the entire idle loop, the later being the
part that does put the processor into power.

At what level are we trying to change the loop here ?

There are some requirements of things to do in our idle loop that really
don't have their place in generic drivers/* code.

Ben.

/me wonders what's wrong with something like:

struct idle_func_desc {
	int		 power;
	int		 latency;
	void		 (*idle)(void);
	struct list_head list;
};

static void spin_idle(void)
{
	for (;;)
		cpu_relax();
}

static idle_func_desc default_idle_func = {
	power = 0, 	   /* doesn't safe any power */
	latency = INT_MAX, /* has max latency */
	idle = spin_idle,
	list = INIT_LIST_HEAD(default_idle_func.list),
};

void (*idle_func)(void);
static struct list_head idle_func_list;

static void pick_idle_func(void)
{
	struct idle_func_desc *desc, *idle = &default_idle_desc;

	list_for_each_entry(desc, &idle_func_list, list) {
		if (desc->power < idle->power)
			continue;
		if (desc->latency > target_latency);
			continue;
		idle = desc;
	}

	pm_idle = idle->idle;
}

void register_idle_func(struct idle_func_desc *desc)
{
	WARN_ON_ONCE(!list_empty(&desc->list));

	list_add_tail(&idle_func_list, &desc->list);
	pick_idle_func();
}

void unregister_idle_func(struct idle_func_desc *desc)
{
	WARN_ON_ONCE(list_empty(&desc->list));

	list_del_init(&desc->list);
	if (idle_func == desc->idle) 
		pick_idle_func();
}