linux-kernel - Re: [PATCH RFC tip/core/rcu 3/4] rcu: Make RCU_FAST_NO

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Date:	Thu, 26 Apr 2012 15:00:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org, "Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 3/4] rcu: Make RCU_FAST_NO_HZ account
 for pauses out of idle

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;


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