linux-kernel - [RFC PATCH 12/15] clocksource: Ignore nohz task cpu in clocksource watchdog

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Message-Id: <1292858662-5650-13-git-send-email-fweisbec@gmail.com>
Date:	Mon, 20 Dec 2010 16:24:19 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: [RFC PATCH 12/15] clocksource: Ignore nohz task cpu in clocksource watchdog

The watchdog should probably make an exception for nohz task cpus
that want to be interrupted the least possible.

However we probably need to warn the user about that.

Another solution would be to make this timer defferable.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Anton Blanchard <anton@....ibm.com>
Cc: Tim Pepper <lnxninja@...ux.vnet.ibm.com>
---
 kernel/time/clocksource.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index c18d7ef..9e62a97 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -302,9 +302,13 @@ static void clocksource_watchdog(unsigned long data)
 	 * Cycle through CPUs to check if the CPUs stay synchronized
 	 * to each other.
 	 */
-	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
-	if (next_cpu >= nr_cpu_ids)
-		next_cpu = cpumask_first(cpu_online_mask);
+	next_cpu = raw_smp_processor_id();
+	do {
+		next_cpu = cpumask_next(next_cpu, cpu_online_mask);
+		if (next_cpu >= nr_cpu_ids)
+			next_cpu = cpumask_first(cpu_online_mask);
+	} while (cpu_has_nohz_task(next_cpu));
+
 	watchdog_timer.expires += WATCHDOG_INTERVAL;
 	add_timer_on(&watchdog_timer, next_cpu);
 out:
-- 
1.7.3.2

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