On Wed, Apr 07 2021 at 10:53, Marcelo Tosatti wrote:
> Setting the realtime clock triggers an IPI to all CPUs to reprogram
> hrtimers.
>
> However, only base, boottime and tai clocks have their offsets updated
base clock? And why boottime? Boottime is not affected by a clock
realtime set. It's clock REALTIME and TAI, nothing else.
> +#define CLOCK_SET_BASES ((1U << HRTIMER_BASE_REALTIME)| \
> + (1U << HRTIMER_BASE_REALTIME_SOFT)| \
> + (1U << HRTIMER_BASE_BOOTTIME)| \
> + (1U << HRTIMER_BASE_BOOTTIME_SOFT)| \
> + (1U << HRTIMER_BASE_TAI)| \
> + (1U << HRTIMER_BASE_TAI_SOFT))
> +
> +static bool need_reprogram_timer(struct hrtimer_cpu_base *cpu_base)
> +{
> + unsigned int active = 0;
> +
> + if (!cpu_base->softirq_activated)
> + active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
> +
> + active = active | (cpu_base->active_bases & HRTIMER_ACTIVE_HARD);
> +
> + if ((active & CLOCK_SET_BASES) == 0)
> + return false;
> +
> + return true;
> +}
Errm.
> + /* Avoid interrupting nohz_full CPUs if possible */
> + preempt_disable();
> + for_each_online_cpu(cpu) {
> + if (tick_nohz_full_cpu(cpu)) {
> + unsigned long flags;
> + struct hrtimer_cpu_base *cpu_base =
> &per_cpu(hrtimer_bases, cpu);
> +
> + raw_spin_lock_irqsave(&cpu_base->lock, flags);
> + if (need_reprogram_timer(cpu_base))
> + cpumask_set_cpu(cpu, mask);
> + else
> + hrtimer_update_base(cpu_base);
> + raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> + }
> + }
How is that supposed to be correct?
CPU0 CPU1
clock_was_set() hrtimer_start(CLOCK_REALTIME)
if (!active_mask[CPU1] & XXX)
continue;
active_mask |= REALTIME;
---> fail because that newly started timer is on the old offset.
Thanks,
tglx
