Marcelo,
On Tue, Apr 13 2021 at 14:04, Marcelo Tosatti wrote:
> Setting the realtime clock triggers an IPI to all CPUs to reprogram
> hrtimers.
s/hrtimers/clock event device/
> However, only realtime and TAI clocks have their offsets updated
> (and therefore potentially require a reprogram).
>
> Check if it only has monotonic active timers, and in that case
boottime != monotonic
> update the realtime and TAI base offsets remotely, skipping the IPI.
Something like this perhaps:
Instead of sending an IPI unconditionally, check each per CPU hrtimer base
whether it has active timers in the CLOCK_REALTIME and CLOCK_TAI bases. If
that's not the case, update the realtime and TAI base offsets remotely and
skip the IPI. This ensures that any subsequently armed timers on
CLOCK_REALTIME and CLOCK_TAI are evaluated with the correct offsets.
Hmm?
> +#define CLOCK_SET_BASES ((1U << HRTIMER_BASE_REALTIME)| \
Missing space between ) and |
> + (1U << HRTIMER_BASE_REALTIME_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)
> + return true;
> +
> + 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;
That's a pretty elaborate way of writing:
return (cpu_base->active_bases & CLOCK_SET_BASES) != 0;
> +}
> +
> /*
> * Clock realtime was set
> *
> @@ -885,9 +907,31 @@ 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 (!zalloc_cpumask_var(&mask, GFP_KERNEL)) {
> + on_each_cpu(retrigger_next_event, NULL, 1);
> + goto set_timerfd;
> + }
> +
> + /* Avoid interrupting CPUs if possible */
> + preempt_disable();
That preempt disable is only required around the function call, for the
loop cpus_read_lock() is sufficient.
> + for_each_online_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);
> + raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> + }
> +
> + smp_call_function_many(mask, retrigger_next_event, NULL, 1);
> + preempt_enable();
> + free_cpumask_var(mask);
> #endif
> +set_timerfd:
My brain compiler tells me that with CONFIG_HIGH_RES_TIMERS=n a real
compiler will emit a warning about a defined, but unused label....
> timerfd_clock_was_set();
> }
Thanks,
tglx
