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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 2:56 PM, Christoph Lameter wrote:
> 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:

Looks good. Did you omit the equivalent fix in clocksource_start_watchdog()
on purpose? For now I just took your change, but tweaked it to add the
equivalent diff with cpumask_first_and() there.

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

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