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SubjectRe: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode)
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On 7/27/2016 11:31 AM, Christoph Lameter wrote:
> 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@linux.com>
>
> 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:

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

Note that you should also cpumask_first_and() in clocksource_start_watchdog(),
just to be complete.

Hopefully the init code runs after tick_init(). It seems like that's probably true.

--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com

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