Re: high power consumption in recent kernels

[Alex,Shi]

Thanks Norbert! 
Mike&Peter:
would you like to add signed-off for the following patch?

---
    sched: nohz_ratelimit function refresh
    
    The nohz_ratelimit() function that written by Mike Galbraith
    can bring about more than 10% throughput for netperf TCP/UDP RR
    when scheduling cross-cpu. It did this by reducing down to nohz
    mode chance.
    But the patch also reduce CPU chance to nohz mode after
    interrupt processed, that cause Norbert's system have 4 watts power
    increase(the system have about 100 int/sec and with a light load).
    That is not acceptable for a laptop.
    
    So, I remove the nohz_ratelimit from irq_exit(). and then the
    Norbert's system back to low power consumption.
    
    Tested-by: Norbert Preining <preining@xxxxxxxx>
    Signed-off-by: Alex Shi <alex.shi@xxxxxxxxx>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1e2a6db..a4dbb37 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -274,8 +274,13 @@ extern cpumask_var_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
 extern void select_nohz_load_balancer(int stop_tick);
 extern int get_nohz_timer_target(void);
+extern int nohz_ratelimit(int cpu);
 #else
 static inline void select_nohz_load_balancer(int stop_tick) { }
+static inline int nohz_ratelimit(int cpu)
+{
+	return 0;
+}
 #endif
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index dc85ceb..132a21c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1182,6 +1182,16 @@ static void resched_task(struct task_struct *p)
 		smp_send_reschedule(cpu);
 }
 
+int nohz_ratelimit(int cpu)
+{
+	struct rq *rq = cpu_rq(cpu);
+	u64 diff = rq->clock - rq->nohz_stamp;
+
+	rq->nohz_stamp = rq->clock;
+
+	return diff < (NSEC_PER_SEC / HZ) >> 1;
+}
+
 static void resched_cpu(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3e216e0..19a7914 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -325,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidle)
 	} while (read_seqretry(&xtime_lock, seq));
 
 	if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
-	    arch_needs_cpu(cpu)) {
+		arch_needs_cpu(cpu) || (inidle && nohz_ratelimit(cpu))) {
 		next_jiffies = last_jiffies + 1;
 		delta_jiffies = 1;
 	} else {


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