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

[Christoph Lameter]

Ok here is a possible patch that explicitly checks for housekeeping cpus:

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

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@xxxxxxxxx>

Index: linux/kernel/time/clocksource.c
===================================================================
--- linux.orig/kernel/time/clocksource.c	2016-07-27 08:41:17.109862517 -0500
+++ linux/kernel/time/clocksource.c	2016-07-27 10:28:31.172447732 -0500
@@ -269,9 +269,12 @@ 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);
-	if (next_cpu >= nr_cpu_ids)
-		next_cpu = cpumask_first(cpu_online_mask);
+	do {
+		next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+		if (next_cpu >= nr_cpu_ids)
+			next_cpu = cpumask_first(cpu_online_mask);
+	} while (!is_housekeeping_cpu(next_cpu));
+
 	watchdog_timer.expires += WATCHDOG_INTERVAL;
 	add_timer_on(&watchdog_timer, next_cpu);
 out: