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From:   Scott Wood <swood@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>
Cc:     linux-kernel@vger.kernel.org, Scott Wood <swood@redhat.com>
Subject: [PATCH v2 1/2] sched/core: Don't skip remote tick for idle cpus
Date:   Sat, 11 Jan 2020 04:53:38 -0500
Message-Id: <1578736419-14628-2-git-send-email-swood@redhat.com>
In-Reply-To: <1578736419-14628-1-git-send-email-swood@redhat.com>
References: <1578736419-14628-1-git-send-email-swood@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

This will be used in the next patch to get a loadavg update from
nohz cpus.  The delta check is skipped because idle_sched_class
doesn't update se.exec_start.

Signed-off-by: Scott Wood <swood@redhat.com>
---
 kernel/sched/core.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 90e4b00ace89..dfb8ea801700 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3668,22 +3668,24 @@ static void sched_tick_remote(struct work_struct *work)
 	 * statistics and checks timeslices in a time-independent way, regardless
 	 * of when exactly it is running.
 	 */
-	if (idle_cpu(cpu) || !tick_nohz_tick_stopped_cpu(cpu))
+	if (!tick_nohz_tick_stopped_cpu(cpu))
 		goto out_requeue;
 
 	rq_lock_irq(rq, &rf);
 	curr = rq->curr;
-	if (is_idle_task(curr) || cpu_is_offline(cpu))
+	if (cpu_is_offline(cpu))
 		goto out_unlock;
 
 	update_rq_clock(rq);
-	delta = rq_clock_task(rq) - curr->se.exec_start;
 
-	/*
-	 * Make sure the next tick runs within a reasonable
-	 * amount of time.
-	 */
-	WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
+	if (!is_idle_task(curr)) {
+		/*
+		 * Make sure the next tick runs within a reasonable
+		 * amount of time.
+		 */
+		delta = rq_clock_task(rq) - curr->se.exec_start;
+		WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
+	}
 	curr->sched_class->task_tick(rq, curr, 0);
 
 out_unlock:
-- 
1.8.3.1