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Message-Id: <20230105005126.1772294-3-paulmck@kernel.org>
Date:   Wed,  4 Jan 2023 16:51:23 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, Zhen Lei <thunder.leizhen@...wei.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 3/6] sched: Add helper nr_context_switches_cpu()

From: Zhen Lei <thunder.leizhen@...wei.com>

Add a function nr_context_switches_cpu() that returns  number of context
switches since boot on the specified CPU.  This information will be used
to diagnose RCU CPU stalls.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Valentin Schneider <vschneid@...hat.com>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/kernel_stat.h | 1 +
 kernel/sched/core.c         | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 898076e173a92..9935f7ecbfb9e 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -52,6 +52,7 @@ DECLARE_PER_CPU(struct kernel_cpustat, kernel_cpustat);
 #define kstat_cpu(cpu) per_cpu(kstat, cpu)
 #define kcpustat_cpu(cpu) per_cpu(kernel_cpustat, cpu)
 
+extern unsigned long long nr_context_switches_cpu(int cpu);
 extern unsigned long long nr_context_switches(void);
 
 extern unsigned int kstat_irqs_cpu(unsigned int irq, int cpu);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 25b582b6ee5f7..2e40a6c116e1c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5282,6 +5282,11 @@ bool single_task_running(void)
 }
 EXPORT_SYMBOL(single_task_running);
 
+unsigned long long nr_context_switches_cpu(int cpu)
+{
+	return cpu_rq(cpu)->nr_switches;
+}
+
 unsigned long long nr_context_switches(void)
 {
 	int i;
-- 
2.31.1.189.g2e36527f23

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