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authorPaul E. McKenney <paul.mckenney@linaro.org>2011-11-28 12:28:34 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-12-11 10:32:07 -0800
commit7cb92499000e3c86dae653077b1465458a039ef6 (patch)
treeebc982a5cc562b4fe0cb8f20541f45a5506a0b5f /kernel/rcutree.h
parent3842a0832a1d6eb0b31421f8810a813135967512 (diff)
downloadlinux-7cb92499000e3c86dae653077b1465458a039ef6.tar.bz2
rcu: Permit dyntick-idle with callbacks pending
The current implementation of RCU_FAST_NO_HZ prevents CPUs from entering dyntick-idle state if they have RCU callbacks pending. Unfortunately, this has the side-effect of often preventing them from entering this state, especially if at least one other CPU is not in dyntick-idle state. However, the resulting per-tick wakeup is wasteful in many cases: if the CPU has already fully responded to the current RCU grace period, there will be nothing for it to do until this grace period ends, which will frequently take several jiffies. This commit therefore permits a CPU that has done everything that the current grace period has asked of it (rcu_pending() == 0) even if it still as RCU callbacks pending. However, such a CPU posts a timer to wake it up several jiffies later (6 jiffies, based on experience with grace-period lengths). This wakeup is required to handle situations that can result in all CPUs being in dyntick-idle mode, thus failing to ever complete the current grace period. If a CPU wakes up before the timer goes off, then it cancels that timer, thus avoiding spurious wakeups. 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/rcutree.h')
-rw-r--r--kernel/rcutree.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 70d8a557090f..9bcfbc9d16c6 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -467,6 +467,8 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg);
#endif /* #ifdef CONFIG_RCU_BOOST */
static void rcu_cpu_kthread_setrt(int cpu, int to_rt);
static void __cpuinit rcu_prepare_kthreads(int cpu);
+static void rcu_prepare_for_idle_init(int cpu);
+static void rcu_cleanup_after_idle(int cpu);
static void rcu_prepare_for_idle(int cpu);
#endif /* #ifndef RCU_TREE_NONCORE */