sched: Add helper nr_context_switches_cpu()

Returns the number of context switches on the specified CPU, which can be
used to diagnose rcu stall.

Signed-off-by: Zhen Lei <[email protected]>

Author: Zhen Lei

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);

kernel/sched/core.c

@@ -5221,6 +5221,11 @@ 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;