linux-kernel - [tip:sched/core] nohz: Allow to check if remote CPU tick is stopped

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Date:   Wed, 21 Feb 2018 02:36:21 -0800
From:   tip-bot for Frederic Weisbecker <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     efault@....de, hpa@...or.com, peterz@...radead.org,
        tglx@...utronix.de, mingo@...nel.org, paulmck@...ux.vnet.ibm.com,
        lcapitulino@...hat.com, linux-kernel@...r.kernel.org,
        cmetcalf@...lanox.com, torvalds@...ux-foundation.org, cl@...ux.com,
        frederic@...nel.org, riel@...hat.com, kernellwp@...il.com
Subject: [tip:sched/core] nohz: Allow to check if remote CPU tick is stopped

Commit-ID:  22ab8bc02a5f6e8ffc418759894f7a6b0b632331
Gitweb:     https://git.kernel.org/tip/22ab8bc02a5f6e8ffc418759894f7a6b0b632331
Author:     Frederic Weisbecker <frederic@...nel.org>
AuthorDate: Wed, 21 Feb 2018 05:17:25 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 21 Feb 2018 09:49:08 +0100

nohz: Allow to check if remote CPU tick is stopped

This check is racy but provides a good heuristic to determine whether
a CPU may need a remote tick or not.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Wanpeng Li <kernellwp@...il.com>
Link: http://lkml.kernel.org/r/1519186649-3242-4-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/tick.h     | 2 ++
 kernel/time/tick-sched.c | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 86576d9..7f8c9a1 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -114,6 +114,7 @@ enum tick_dep_bits {
 #ifdef CONFIG_NO_HZ_COMMON
 extern bool tick_nohz_enabled;
 extern bool tick_nohz_tick_stopped(void);
+extern bool tick_nohz_tick_stopped_cpu(int cpu);
 extern void tick_nohz_idle_enter(void);
 extern void tick_nohz_idle_exit(void);
 extern void tick_nohz_irq_exit(void);
@@ -125,6 +126,7 @@ extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
 #else /* !CONFIG_NO_HZ_COMMON */
 #define tick_nohz_enabled (0)
 static inline int tick_nohz_tick_stopped(void) { return 0; }
+static inline int tick_nohz_tick_stopped_cpu(int cpu) { return 0; }
 static inline void tick_nohz_idle_enter(void) { }
 static inline void tick_nohz_idle_exit(void) { }
 
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 0aba041..d479b21 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -486,6 +486,13 @@ bool tick_nohz_tick_stopped(void)
 	return __this_cpu_read(tick_cpu_sched.tick_stopped);
 }
 
+bool tick_nohz_tick_stopped_cpu(int cpu)
+{
+	struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
+
+	return ts->tick_stopped;
+}
+
 /**
  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
  *