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Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode)

From Christoph Lameter <cl@linux.com>
Newsgroups linux.kernel
Subject Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode)
Date 2016-07-27 21:00 +0200
Message-ID <rZCdH-3d7-11@gated-at.bofh.it> (permalink)
References (6 earlier) <rZxxo-6F-9@gated-at.bofh.it> <rZyWu-19P-23@gated-at.bofh.it> <rZyWu-19P-21@gated-at.bofh.it> <rZz6a-1cX-7@gated-at.bofh.it> <rZCdH-3d7-13@gated-at.bofh.it>
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On Wed, 27 Jul 2016, Chris Metcalf wrote:

> How about using cpumask_next_and(raw_smp_processor_id(), cpu_online_mask,
> housekeeping_cpumask()), likewise cpumask_first_and()?  Does that work?

Ok here is V2:


Subject: clocksource: Do not schedule watchdog on isolated or NOHZ cpus V2

watchdog checks can only run on housekeeping capable cpus. Otherwise
we will be generating noise that we would like to avoid on the isolated
processors.

Signed-off-by: Christoph Lameter <cl@linux.com>

Index: linux/kernel/time/clocksource.c
===================================================================
--- linux.orig/kernel/time/clocksource.c
+++ linux/kernel/time/clocksource.c
@@ -269,9 +269,10 @@ static void clocksource_watchdog(unsigne
 	 * Cycle through CPUs to check if the CPUs stay synchronized
 	 * to each other.
 	 */
-	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+	next_cpu = cpumask_next_and(raw_smp_processor_id(), cpu_online_mask, housekeeping_cpumask());
 	if (next_cpu >= nr_cpu_ids)
-		next_cpu = cpumask_first(cpu_online_mask);
+		next_cpu = cpumask_first_and(cpu_online_mask, housekeeping_cpumask());
+
 	watchdog_timer.expires += WATCHDOG_INTERVAL;
 	add_timer_on(&watchdog_timer, next_cpu);
 out:

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Thread

clocksource_watchdog causing scheduling of timers every second (was  [v13] support "task_isolation" mode) Christoph Lameter <cl@linux.com> - 2016-07-27 16:00 +0200
  Re: clocksource_watchdog causing scheduling of timers every second  (was [v13] support "task_isolation" mode) Christoph Lameter <cl@linux.com> - 2016-07-27 17:30 +0200
    Re: clocksource_watchdog causing scheduling of timers every second  (was [v13] support "task_isolation" mode) Christoph Lameter <cl@linux.com> - 2016-07-27 17:40 +0200
      Re: clocksource_watchdog causing scheduling of timers every second  (was [v13] support "task_isolation" mode) Christoph Lameter <cl@linux.com> - 2016-07-27 21:00 +0200
        Re: clocksource_watchdog causing scheduling of timers every second  (was [v13] support "task_isolation" mode) Christoph Lameter <cl@linux.com> - 2016-07-27 22:00 +0200
          Re: clocksource_watchdog causing scheduling of timers every second  (was [v13] support "task_isolation" mode) Francis Giraldeau <francis.giraldeau@gmail.com> - 2016-07-29 20:40 +0200

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