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SubjectRe: [PATCH 7/8] nohz: Evaluate tick dependency once on context switch
On Thu, Jun 11, 2015 at 07:36:07PM +0200, Frederic Weisbecker wrote:
> +static void tick_nohz_full_update_dependencies(void)
> +{
> + struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
> +
> + if (!posix_cpu_timers_can_stop_tick(current))
> + ts->tick_needed |= TICK_NEEDED_POSIX_CPU_TIMER;
> +
> + if (!perf_event_can_stop_tick())
> + ts->tick_needed |= TICK_NEEDED_PERF_EVENT;
> +
> + if (!sched_can_stop_tick())
> + ts->tick_needed |= TICK_NEEDED_SCHED;
>
> #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
> /*
> + * sched_clock_tick() needs us?
> + *
> * TODO: kick full dynticks CPUs when
> * sched_clock_stable is set.
> */
> if (!sched_clock_stable()) {
> + ts->tick_needed |= TICK_NEEDED_CLOCK_UNSTABLE;
> /*
> * Don't allow the user to think they can get
> * full NO_HZ with this machine.
> */
> WARN_ONCE(tick_nohz_full_running,
> "NO_HZ FULL will not work with unstable sched clock");
> }
> #endif
> }

Colour me confused; why does this function exist at all? Should not
these bits be managed by those respective subsystems?


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