linux-kernel - [PATCH 1/3] sched: define a function to report the number of context switches on a CPU

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Date:   Mon, 19 Aug 2019 23:14:27 -0700
From:   longli@...uxonhyperv.com
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Long Li <longli@...rosoft.com>
Subject: [PATCH 1/3] sched: define a function to report the number of context switches on a CPU

From: Long Li <longli@...rosoft.com>

The number of context switches on a CPU is useful to determine how busy this
CPU is on processing IRQs. Export this information so it can be used by device
drivers.

Signed-off-by: Long Li <longli@...rosoft.com>
---
 include/linux/sched.h | 1 +
 kernel/sched/core.c   | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9b35aff09f70..575f1ef7b159 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1500,6 +1500,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
 
 extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
 extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);
+extern u64 get_cpu_rq_switches(int cpu);
 #ifdef CONFIG_SMP
 extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
 extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4a8e7207cafa..1a76f0e97c2d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1143,6 +1143,12 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 }
 EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
 
+u64 get_cpu_rq_switches(int cpu)
+{
+	return cpu_rq(cpu)->nr_switches;
+}
+EXPORT_SYMBOL_GPL(get_cpu_rq_switches);
+
 void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 {
 #ifdef CONFIG_SCHED_DEBUG
-- 
2.17.1