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

[Chris Metcalf]

On 7/27/2016 9:55 AM, Christoph Lameter wrote:
> The critical piece of code is this:
>
>          /*
>           * 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);
>          watchdog_timer.expires += WATCHDOG_INTERVAL;
>          add_timer_on(&watchdog_timer, next_cpu);
>
>
> Should we just cycle through the cpus that are not isolated? Otherwise we
> need to have some means to check the clocksources for accuracy remotely
> (probably impossible for TSC etc).

That sounds like the right idea - use the housekeeping cpu mask instead of the
cpu online mask.  Should be a straightforward patch; do you want to do that
and test it in your configuration, and I'll include it in the next spin of the
patch series?

Thanks for your testing!

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