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Subject[PATCH] rcu: Report a quiescent state when it's exactly in the state
Date
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>
---
include/linux/rcupdate.h | 4 ++--
kernel/rcu/tiny.c | 6 +++---
kernel/rcu/tree.c | 4 ++--
3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index ee8cf5fc..7432261 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -195,8 +195,8 @@ 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); \
+ rcu_note_voluntary_context_switch_lite(current); \
+ cond_resched(); \
} while (0)

/*
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index a64eee0..68d2332 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -120,12 +120,12 @@ void rcu_bh_qs(void)
*/
void rcu_check_callbacks(int user)
{
- if (user)
+ if (user) {
rcu_sched_qs();
- else if (!in_softirq())
rcu_bh_qs();
- if (user)
rcu_note_voluntary_context_switch(current);
+ } else if (!in_softirq())
+ rcu_bh_qs();
}

/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 36075dd..1abe29a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2595,6 +2595,7 @@ void rcu_check_callbacks(int user)

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

} else if (!in_softirq()) {

@@ -2610,8 +2611,7 @@ 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"));
}

--
1.9.1
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