linux-kernel - [PATCH v4 tip/core/rcu 33/38] rcu-tasks: Add count for idle tasks on offline CPUs

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Message-Id: <20200415181941.11653-33-paulmck@kernel.org>
Date:   Wed, 15 Apr 2020 11:19:36 -0700
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH v4 tip/core/rcu 33/38] rcu-tasks: Add count for idle tasks on offline CPUs

From: "Paul E. McKenney" <paulmck@...nel.org>

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@...nel.org>
---
 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 b51f19a..43cac4b 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);
@@ -1152,7 +1155,8 @@ 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);
-- 
2.9.5