On Wed, Apr 07, 2021 at 10:53:01AM -0300, 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
> (and therefore potentially require a reprogram).
>
> If the CPU is a nohz_full one, check if it only has
> monotonic active timers, and in that case update the
> realtime base offsets, skipping the IPI.
>
> This reduces interruptions to nohz_full CPUs.
>
> Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 743c852e10f2..b42b1a434b22 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -853,6 +853,28 @@ static void hrtimer_reprogram(struct hrtimer *timer,
> bool reprogram)
> tick_program_event(expires, 1);
> }
>
> +#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;
> +}
> +
> /*
> * Clock realtime was set
> *
> @@ -867,9 +889,41 @@ static void hrtimer_reprogram(struct hrtimer *timer,
> bool reprogram)
> void clock_was_set(void)
> {
> #ifdef CONFIG_HIGH_RES_TIMERS
> - /* Retrigger the CPU local events everywhere */
> - on_each_cpu(retrigger_next_event, NULL, 1);
> + cpumask_var_t mask;
> + int cpu;
> +
> + if (!tick_nohz_full_enabled()) {
> + /* Retrigger the CPU local events everywhere */
> + on_each_cpu(retrigger_next_event, NULL, 1);
> + goto set_timerfd;
> + }
> +
> + if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
> + on_each_cpu(retrigger_next_event, NULL, 1);
> + goto set_timerfd;
> + }
> +
> + /* 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);
> + }
You forgot to add the housekeeping CPUs to the mask.
As for the need_reprogram_timer() trick, I'll rather defer to Thomas review...
Thanks.
> + }
> +
> + smp_call_function_many(mask, retrigger_next_event, NULL, 1);
> + preempt_enable();
> + free_cpumask_var(mask);
> #endif
> +set_timerfd:
> timerfd_clock_was_set();
> }
>
>
