Commit 07f27570 authored May 11, 2018 by Byungchul Park Committed by Paul E. McKenney Jul 12, 2018

rcu: Improve rcu_note_voluntary_context_switch() reporting



We expect a quiescent state of TASKS_RCU when cond_resched_tasks_rcu_qs()
is called, no matter whether it actually be scheduled or not. However,
it currently doesn't report the quiescent state when the task enters
into __schedule() as it's called with preempt = true. So make it report
the quiescent state unconditionally when cond_resched_tasks_rcu_qs() is
called.

And in TINY_RCU, even though the quiescent state of rcu_bh also should
be reported when the tick interrupt comes from user, it doesn't. So make
it reported.

Lastly in TREE_RCU, rcu_note_voluntary_context_switch() should be
reported when the tick interrupt comes from not only user but also idle,
as an extended quiescent state.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Simplify rcutiny portion given no RCU-tasks for !PREEMPT. ]

parent 3949fa9b

include/linux/rcupdate.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -194,8 +194,8 @@ static inline void exit_tasks_rcu_finish(void) { }
		*/
		#define cond_resched_tasks_rcu_qs() \
		do { \
		if (!cond_resched()) \
		rcu_note_voluntary_context_switch_lite(current); \
		cond_resched(); \
		} while (0)

		/*

kernel/rcu/tiny.c

+1 −3

Original line number	Diff line number	Diff line
		@@ -122,10 +122,8 @@ void rcu_check_callbacks(int user)
		{
		if (user)
		rcu_sched_qs();
		else if (!in_softirq())
		if (user \|\| !in_softirq())
		rcu_bh_qs();
		if (user)
		rcu_note_voluntary_context_switch(current);
		}

		/*

kernel/rcu/tree.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2645,6 +2645,7 @@ void rcu_check_callbacks(int user)

		rcu_sched_qs();
		rcu_bh_qs();
		rcu_note_voluntary_context_switch(current);

		} else if (!in_softirq()) {

		@@ -2660,8 +2661,7 @@ void rcu_check_callbacks(int user)
		rcu_preempt_check_callbacks();
		if (rcu_pending())
		invoke_rcu_core();
		if (user)
		rcu_note_voluntary_context_switch(current);

		trace_rcu_utilization(TPS("End scheduler-tick"));
		}