sched/fair: Remove #ifdefs from scale_rt_capacity()

Reuse cpu_util_irq() that has been defined for schedutil and set irq util
to 0 when !CONFIG_IRQ_TIME_ACCOUNTING.

But the compiler is not able to optimize the sequence (at least with
aarch64 GCC 7.2.1):

	free *= (max - irq);
	free /= max;

when irq is fixed to 0

Add a new inline function scale_irq_capacity() that will scale utilization
when irq is accounted. Reuse this funciton in schedutil which applies
similar formula.

Suggested-by: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: rjw@rjwysocki.net
Link: http://lkml.kernel.org/r/1532001606-6689-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -177,7 +177,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 
 	rq->clock_task += delta;
 
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+#ifdef HAVE_SCHED_AVG_IRQ
 	if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
 		update_irq_load_avg(rq, irq_delta + steal);
 #endif

kernel/sched/cpufreq_schedutil.c

@@ -247,8 +247,7 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
 	 *   U' = irq + ------- * U
 	 *                max
 	 */
-	util *= (max - irq);
-	util /= max;
+	util = scale_irq_capacity(util, irq, max);
 	util += irq;
 
 	/*

kernel/sched/fair.c

@@ -7551,16 +7551,12 @@ static unsigned long scale_rt_capacity(int cpu)
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long max = arch_scale_cpu_capacity(NULL, cpu);
 	unsigned long used, free;
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
 	unsigned long irq;
-#endif
 
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
-	irq = READ_ONCE(rq->avg_irq.util_avg);
+	irq = cpu_util_irq(rq);
 
 	if (unlikely(irq >= max))
 		return 1;
-#endif
 
 	used = READ_ONCE(rq->avg_rt.util_avg);
 	used += READ_ONCE(rq->avg_dl.util_avg);
@@ -7569,11 +7565,8 @@ static unsigned long scale_rt_capacity(int cpu)
 		return 1;
 
 	free = max - used;
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
-	free *= (max - irq);
-	free /= max;
-#endif
-	return free;
+
+	return scale_irq_capacity(free, irq, max);
 }
 
 static void update_cpu_capacity(struct sched_domain *sd, int cpu)

kernel/sched/sched.h

@@ -856,6 +856,7 @@ struct rq {
 	struct sched_avg	avg_rt;
 	struct sched_avg	avg_dl;
 #if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+#define HAVE_SCHED_AVG_IRQ
 	struct sched_avg	avg_irq;
 #endif
 	u64			idle_stamp;
@@ -2210,17 +2211,32 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
 {
 	return READ_ONCE(rq->avg_rt.util_avg);
 }
+#endif
 
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+#ifdef HAVE_SCHED_AVG_IRQ
 static inline unsigned long cpu_util_irq(struct rq *rq)
 {
 	return rq->avg_irq.util_avg;
 }
+
+static inline
+unsigned long scale_irq_capacity(unsigned long util, unsigned long irq, unsigned long max)
+{
+	util *= (max - irq);
+	util /= max;
+
+	return util;
+
+}
 #else
 static inline unsigned long cpu_util_irq(struct rq *rq)
 {
 	return 0;
 }
 
-#endif
+static inline
+unsigned long scale_irq_capacity(unsigned long util, unsigned long irq, unsigned long max)
+{
+	return util;
+}
 #endif