commit 15ba0ba860871cf74b48b1bb47c26c91a66126f3
author Paul E. McKenney <paul.mckenney@linaro.org> Wed Apr 06 16:01:16 2011 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> Thu May 05 23:16:56 2011 -0700
tree 2043eeca7d6df62fc0ae918b61abada073f81415
parent a9f4793d8900dc5dc09b3951bdcd4731290e06fe

rcu: add grace-period age and more kthread state to tracing

This commit adds the age in jiffies of the current grace period along
with the duration in jiffies of the longest grace period since boot
to the rcu/rcugp debugfs file.  It also adds an additional "O" state
to kthread tracing to differentiate between the kthread waiting due to
having nothing to do on the one hand and waiting due to being on the
wrong CPU on the other hand.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutree.c

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index bb84dec..27b6d8d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -92,6 +92,7 @@
  */
 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
+DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
 static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
 DEFINE_PER_CPU(char, rcu_cpu_has_work);
 static char rcu_kthreads_spawnable;
@@ -888,6 +889,8 @@
 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
 	__releases(rcu_get_root(rsp)->lock)
 {
+	unsigned long gp_duration;
+
 	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
 
 	/*
@@ -895,6 +898,9 @@
 	 * is seen before the assignment to rsp->completed.
 	 */
 	smp_mb(); /* See above block comment. */
+	gp_duration = jiffies - rsp->gp_start;
+	if (gp_duration > rsp->gp_max)
+		rsp->gp_max = gp_duration;
 	rsp->completed = rsp->gpnum;
 	rsp->signaled = RCU_GP_IDLE;
 	rcu_start_gp(rsp, flags);  /* releases root node's rnp->lock. */
@@ -1583,12 +1589,15 @@
 	       smp_processor_id() != cpu) {
 		if (kthread_should_stop())
 			return 1;
+		per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+		per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
 		local_bh_enable();
 		schedule_timeout_uninterruptible(1);
 		if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
 			set_cpus_allowed_ptr(current, cpumask_of(cpu));
 		local_bh_disable();
 	}
+	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
 	return 0;
 }
 
@@ -1656,6 +1665,7 @@
 	if (IS_ERR(t))
 		return PTR_ERR(t);
 	kthread_bind(t, cpu);
+	per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
 	WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
 	per_cpu(rcu_cpu_kthread_task, cpu) = t;
 	wake_up_process(t);