[tip: core/rcu] rcu-tasks: Add count for idle tasks on offline CPUs

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     edf3775f0ad66879796f594983163f672c4bf1a2
Gitweb:        https://git.kernel.org/tip/edf3775f0ad66879796f594983163f672c4bf1a2
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Sun, 22 Mar 2020 14:09:45 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 27 Apr 2020 11:03:53 -07:00

rcu-tasks: Add count for idle tasks on offline CPUs

This commit adds a counter for the number of times the quiescent state
was an idle task associated with an offline CPU, and prints this count
at the end of rcutorture runs and at stall time.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tasks.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index ce65883..0d1b5bf 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -729,6 +729,7 @@ static DEFINE_PER_CPU(bool, trc_ipi_to_cpu);
 // heavyweight readers executing explicit memory barriers.
 unsigned long n_heavy_reader_attempts;
 unsigned long n_heavy_reader_updates;
+unsigned long n_heavy_reader_ofl_updates;
 
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
 DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
@@ -840,6 +841,8 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
 		    !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
 			return false; // No quiescent state, do it the hard way.
 		n_heavy_reader_updates++;
+		if (ofl)
+			n_heavy_reader_ofl_updates++;
 		in_qs = true;
 	} else {
 		in_qs = likely(!t->trc_reader_nesting);
@@ -1156,7 +1159,8 @@ static void show_rcu_tasks_trace_gp_kthread(void)
 {
 	char buf[64];
 
-	sprintf(buf, "N%d h:%lu/%lu", atomic_read(&trc_n_readers_need_end),
+	sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end),
+		data_race(n_heavy_reader_ofl_updates),
 		data_race(n_heavy_reader_updates),
 		data_race(n_heavy_reader_attempts));
 	show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf);