path: root/kernel
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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-05-03 15:38:10 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-05-09 14:26:57 -0700
commit98248a0e24327bc64eb7518145c44bff7bebebc3 (patch)
tree5ec88465d949558e42e83fd8321c725614c00269 /kernel
parent21e52e15666323078b8517a4312712579176b56f (diff)
rcu: Explicitly initialize RCU_FAST_NO_HZ per-CPU variables
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>
Diffstat (limited to 'kernel')
1 files changed, 16 insertions, 4 deletions
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index bbb43cad755..7082ea93566 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -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_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
+/* Loop counter for rcu_prepare_for_idle(). */
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);
+/* Timer to awaken the CPU if it enters dyntick-idle mode with callbacks. */
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);
+/* Enable special processing on first attempt to enter dyntick-idle mode. */
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);
+/* Snapshot of rcu_nonlazy_posted to detect meaningful exits from idle. */
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)
+ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
setup_timer(&per_cpu(rcu_idle_gp_timer, 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()
- * can detect when something out of the idle loop posts a callback.
- * Of course, it had better do so either from a trace event designed to
- * be called from idle or from within RCU_NONIDLE().
+ * Keep a running count of the number of non-lazy callbacks posted
+ * on this CPU. This running counter (which is never decremented) allows
+ * rcu_prepare_for_idle() to detect when something out of the idle loop
+ * 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)