sched: Add helper kstat_cpu_softirqs_sum()

Add a kstat_cpu_softirqs_sum() function that is similar to
kstat_cpu_irqs_sum(), but which counts software interrupts since boot
on the specified CPU.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Josh Don <joshdon@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Peter Zijlstra (Intel)"
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

include/linux/kernel_stat.h

@@ -67,6 +67,17 @@ static inline unsigned int kstat_softirqs_cpu(unsigned int irq, int cpu)
        return kstat_cpu(cpu).softirqs[irq];
 }
 
+static inline unsigned int kstat_cpu_softirqs_sum(int cpu)
+{
+	int i;
+	unsigned int sum = 0;
+
+	for (i = 0; i < NR_SOFTIRQS; i++)
+		sum += kstat_softirqs_cpu(i, cpu);
+
+	return sum;
+}
+
 /*
  * Number of interrupts per specific IRQ source, since bootup
  */