linux-kernel - [patch 6/7] tick/sched: Release seqcount before invoking calc_load

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Message-Id: <20201117132006.660902274@linutronix.de>
Date:   Tue, 17 Nov 2020 14:19:48 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Yunfeng Ye <yeyunfeng@...wei.com>
Subject: [patch 6/7] tick/sched: Release seqcount before invoking calc_load_global()

calc_load_global() does not need the sequence count protection.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/time/tick-sched.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -20,6 +20,7 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/stat.h>
 #include <linux/sched/nohz.h>
+#include <linux/sched/loadavg.h>
 #include <linux/module.h>
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
@@ -107,7 +108,8 @@ static void tick_do_update_jiffies64(kti
 						tick_period);
 	}
 
-	do_timer(ticks);
+	/* Advance jiffies to complete the jiffies_seq protected job */
+	jiffies_64 += ticks;
 
 	/*
 	 * Keep the tick_next_period variable up to date.  WRITE_ONCE()
@@ -116,7 +118,15 @@ static void tick_do_update_jiffies64(kti
 	WRITE_ONCE(tick_next_period,
 		   ktime_add(last_jiffies_update, tick_period));
 
+	/*
+	 * Release the sequence count. calc_global_load() below is not
+	 * protected by it, but jiffies_lock needs to be held to prevent
+	 * concurrent invocations.
+	 */
 	write_seqcount_end(&jiffies_seq);
+
+	calc_global_load();
+
 	raw_spin_unlock(&jiffies_lock);
 	update_wall_time();
 }