Re: [PATCH RFC tip/core/rcu 3/4] rcu: Make RCU_FAST_NO_HZ account for pauses out of idle

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2012-04-23 at 09:16 -0700, Paul E. McKenney wrote:
>  static DEFINE_PER_CPU(int, rcu_dyntick_drain);
>  static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
>  static DEFINE_PER_CPU(struct timer_list, rcu_idle_gp_timer);
> +static DEFINE_PER_CPU(unsigned long, rcu_idle_gp_timer_expires);
> +static DEFINE_PER_CPU(bool, rcu_idle_first_pass);
> +static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted);
> +static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted_snap);


Wouldn't that all be prettier if it were in a struct of sorts?

struct rcu_dyntick {
	int			drain;
	unsigned long		holdoff;
	struct timer_list	gp_timer;
	unsigned long		gp_timer_expires;
	bool			first_pass;
	unsigned long		posted;
	unsigned long		posted_snap;
};

static DEFINE_PER_CPU(struct rcu_dyntick, rcu_dyntick);

( fwiw, bool doesn't have a well specified storage type )

This way you have more control over the placement, variables are forced
to be together, instead of at the mercy of whatever per_cpu and the
linker do, and you more clearly see the holes in the structure.

All the per_cpu() usage should still work like:

  per_cpu(rcu_dyntick.first_pass, cpu) = 0;