linux-kernel - Re: [PATCH] sched/fair: remove #ifdefs from scale_rt

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Message-ID: <20180720123146.GL2476@hirez.programming.kicks-ass.net>
Date:   Fri, 20 Jul 2018 14:31:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org
Subject: Re: [PATCH] sched/fair: remove #ifdefs from scale_rt_capacity

On Thu, Jul 19, 2018 at 02:00:06PM +0200, Vincent Guittot wrote:
> 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

So much for compilers.... I though those things were supposed to be
'clever'.

> +#if defined(SMP) \
> + && (defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING))

That's atrocious :-)

Fixed it with the below.


--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -135,7 +135,7 @@ static void update_rq_clock_task(struct
  * In theory, the compile should just see 0 here, and optimize out the call
  * to sched_rt_avg_update. But I don't trust it...
  */
-#if defined(CONFIG_IRQ_TIME_ACCOUNTING) || defined(CONFIG_PARAVIRT_TIME_ACCOUNTING)
+#ifdef HAVE_SCHED_AVG_IRQ
 	s64 steal = 0, irq_delta = 0;
 #endif
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
@@ -177,7 +177,7 @@ static void update_rq_clock_task(struct
 
 	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
--- a/kernel/sched/sched.h
+++ b/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;
@@ -2212,8 +2213,7 @@ static inline unsigned long cpu_util_rt(
 }
 #endif
 
-#if defined(SMP) \
- && (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;