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rcu: Explicitly initialize RCU_FAST_NO_HZ per-CPU variables

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The current initialization of the RCU_FAST_NO_HZ per-CPU variables makes
needless and fragile assumptions about the initial value of things like
the jiffies counter.  This commit therefore explicitly initializes all of
them that are better started with a non-zero value.  It also adds some
comments describing the per-CPU state variables.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-05-03 15:38:10 -07:00 committed by Paul E. McKenney
parent 21e52e1566
commit 98248a0e24
1 changed files with 16 additions and 4 deletions
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20
kernel/rcutree_plugin.h
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@ -1986,12 +1986,19 @@ static void rcu_idle_count_callbacks_posted(void)
#define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */ #define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
/* Loop counter for rcu_prepare_for_idle(). */
static DEFINE_PER_CPU(int, rcu_dyntick_drain); static DEFINE_PER_CPU(int, rcu_dyntick_drain);
/* If rcu_dyntick_holdoff==jiffies, don't try to enter dyntick-idle mode. */
static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
/* Timer to awaken the CPU if it enters dyntick-idle mode with callbacks. */
static DEFINE_PER_CPU(struct timer_list, rcu_idle_gp_timer); static DEFINE_PER_CPU(struct timer_list, rcu_idle_gp_timer);
/* Scheduled expiry time for rcu_idle_gp_timer to allow reposting. */
static DEFINE_PER_CPU(unsigned long, rcu_idle_gp_timer_expires); static DEFINE_PER_CPU(unsigned long, rcu_idle_gp_timer_expires);
/* Enable special processing on first attempt to enter dyntick-idle mode. */
static DEFINE_PER_CPU(bool, rcu_idle_first_pass); static DEFINE_PER_CPU(bool, rcu_idle_first_pass);
/* Running count of non-lazy callbacks posted, never decremented. */
static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted); static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted);
/* Snapshot of rcu_nonlazy_posted to detect meaningful exits from idle. */
static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted_snap); static DEFINE_PER_CPU(unsigned long, rcu_nonlazy_posted_snap);
/* /*
@ -2092,8 +2099,11 @@ static void rcu_idle_gp_timer_func(unsigned long cpu_in)
*/ */
static void rcu_prepare_for_idle_init(int cpu) static void rcu_prepare_for_idle_init(int cpu)
{ {
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
setup_timer(&per_cpu(rcu_idle_gp_timer, cpu), setup_timer(&per_cpu(rcu_idle_gp_timer, cpu),
rcu_idle_gp_timer_func, cpu); rcu_idle_gp_timer_func, cpu);
per_cpu(rcu_idle_gp_timer_expires, cpu) = jiffies - 1;
per_cpu(rcu_idle_first_pass, cpu) = 1;
} }
/* /*
@ -2232,10 +2242,12 @@ static void rcu_prepare_for_idle(int cpu)
} }
/* /*
* Keep a running count of callbacks posted so that rcu_prepare_for_idle() * Keep a running count of the number of non-lazy callbacks posted
* can detect when something out of the idle loop posts a callback. * on this CPU. This running counter (which is never decremented) allows
* Of course, it had better do so either from a trace event designed to * rcu_prepare_for_idle() to detect when something out of the idle loop
* be called from idle or from within RCU_NONIDLE(). * posts a callback, even if an equal number of callbacks are invoked.
* Of course, callbacks should only be posted from within a trace event
* designed to be called from idle or from within RCU_NONIDLE().
*/ */
static void rcu_idle_count_callbacks_posted(void) static void rcu_idle_count_callbacks_posted(void)
{ {