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

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 <redacted>

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: