linux-kernel - [PATCH v2] sched: Drop outdated compile-optimization

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Date:   Fri, 17 Jun 2022 13:34:58 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Valentin Schneider <vschneid@...hat.com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH v2] sched: Drop outdated compile-optimization

Looks like this exists from way back in 2011 (commit 095c0aa83e52
("sched: adjust scheduler cpu power for stolen time")), when there was a
little more aggressive use of #if around these variables. The comment
mostly serves to confuse the reader, although it may arguably apply to
the (excessive) #ifdef CONFIG_HAVE_SCHED_AVG_IRQ.

Anyway, the #ifdef is not needed, so drop both the comment and the
"optimization." Any modern compiler will realize this block is not
needed (for one, update_irq_load_avg() is an empty function when
!CONFIG_HAVE_SCHED_AVG_IRQ).

Confirmed on:

  x86 gcc 11.2.0 (Debian)
  x86 clang 13.0.1 (Debian)
  aarch64-linux-gnu-gcc 11.2.0 (Debian)

Signed-off-by: Brian Norris <briannorris@...omium.org>
---

Changes in v2:
 - drop #ifdef too

 kernel/sched/core.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bfa7452ca92e..eced503aa670 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -679,10 +679,6 @@ struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
 
 static void update_rq_clock_task(struct rq *rq, s64 delta)
 {
-/*
- * 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...
- */
 	s64 __maybe_unused steal = 0, irq_delta = 0;
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
@@ -724,10 +720,9 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
 
 	rq->clock_task += delta;
 
-#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
 	if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
 		update_irq_load_avg(rq, irq_delta + steal);
-#endif
+
 	update_rq_clock_pelt(rq, delta);
 }
 
-- 
2.36.1.476.g0c4daa206d-goog