On Fri, 2013-12-20 at 16:41 +0100, Sebastian Andrzej Siewior wrote:
> On 07.11.13, Thomas Gleixner wrote:
> > below should address that issue. If that works on mainline we can
> > adapt it for RT (needs a trylock(&base->lock) there).
>
> okay, so this is waht I'm going to take for -RT:
Works, modulo noisy workqueues.
rtbox:~ # sleep 35 && killall pert& cgexec -g cpuset:rtcpus taskset -c 3 pert 5
[1] 5660
2400.05 MHZ CPU
perturbation threshold 0.018 usecs.
pert/s: 33 >15.75us: 2 min: 0.04 max: 24.14 avg: 2.51 sum/s: 84us overhead: 0.01%
pert/s: 35 >15.54us: 3 min: 0.04 max: 24.89 avg: 2.39 sum/s: 84us overhead: 0.01%
pert/s: 30 >15.27us: 2 min: 0.04 max: 23.03 avg: 2.64 sum/s: 80us overhead: 0.01%
pert/s: 34 >15.12us: 3 min: 0.04 max: 25.03 avg: 2.51 sum/s: 86us overhead: 0.01%
pert/s: 31 >14.93us: 2 min: 0.04 max: 23.86 avg: 2.60 sum/s: 83us overhead: 0.01%
Terminated
> diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
> index 79a7a35..bdbf77db 100644
> --- a/include/linux/hrtimer.h
> +++ b/include/linux/hrtimer.h
> @@ -461,9 +461,8 @@ extern int schedule_hrtimeout_range_clock(ktime_t *expires,
> unsigned long delta, const enum hrtimer_mode mode, int clock);
> extern int schedule_hrtimeout(ktime_t *expires, const enum hrtimer_mode mode);
>
> -/* Soft interrupt function to run the hrtimer queues: */
> +/* Called from the periodic timer tick */
> extern void hrtimer_run_queues(void);
> -extern void hrtimer_run_pending(void);
>
> /* Bootup initialization: */
> extern void __init hrtimers_init(void);
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index c383841..7aa442e 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1694,30 +1694,6 @@ static void run_hrtimer_softirq(struct softirq_action *h)
> }
>
> /*
> - * Called from timer softirq every jiffy, expire hrtimers:
> - *
> - * For HRT its the fall back code to run the softirq in the timer
> - * softirq context in case the hrtimer initialization failed or has
> - * not been done yet.
> - */
> -void hrtimer_run_pending(void)
> -{
> - if (hrtimer_hres_active())
> - return;
> -
> - /*
> - * This _is_ ugly: We have to check in the softirq context,
> - * whether we can switch to highres and / or nohz mode. The
> - * clocksource switch happens in the timer interrupt with
> - * xtime_lock held. Notification from there only sets the
> - * check bit in the tick_oneshot code, otherwise we might
> - * deadlock vs. xtime_lock.
> - */
> - if (tick_check_oneshot_change(!hrtimer_is_hres_enabled()))
> - hrtimer_switch_to_hres();
> -}
> -
> -/*
> * Called from hardirq context every jiffy
> */
> void hrtimer_run_queues(void)
> @@ -1730,6 +1706,13 @@ void hrtimer_run_queues(void)
> if (hrtimer_hres_active())
> return;
>
> + /*
> + * Check whether we can switch to highres mode.
> + */
> + if (tick_check_oneshot_change(!hrtimer_is_hres_enabled())
> + && hrtimer_switch_to_hres())
> + return;
> +
> for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
> base = &cpu_base->clock_base[index];
> if (!timerqueue_getnext(&base->active))
> diff --git a/kernel/timer.c b/kernel/timer.c
> index b06c647..46467be 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1443,8 +1443,6 @@ static void run_timer_softirq(struct softirq_action *h)
> irq_work_run();
> #endif
>
> - hrtimer_run_pending();
> -
> if (time_after_eq(jiffies, base->timer_jiffies))
> __run_timers(base);
> }
> @@ -1454,8 +1452,27 @@ static void run_timer_softirq(struct softirq_action *h)
> */
> void run_local_timers(void)
> {
> + struct tvec_base *base = __this_cpu_read(tvec_bases);
> +
> hrtimer_run_queues();
> - raise_softirq(TIMER_SOFTIRQ);
> + /*
> + * We can access this lockless as we are in the timer
> + * interrupt. If there are no timers queued, nothing to do in
> + * the timer softirq.
> + */
> + if (!spin_do_trylock(&base->lock)) {
> + raise_softirq(TIMER_SOFTIRQ);
> + return;
> + }
> + if (!base->active_timers)
> + goto out;
> +
> + /* Check whether the next pending timer has expired */
> + if (time_before_eq(base->next_timer, jiffies))
> + raise_softirq(TIMER_SOFTIRQ);
> +out:
> + rt_spin_unlock_after_trylock_in_irq(&base->lock);
> +
> }
>
> #ifdef __ARCH_WANT_SYS_ALARM
--
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