Date:	Sat, 08 Nov 2014 03:05:56 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Brown, Len" <len.brown@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	"linux-pm@...r.kernel.org >> Linux PM list" 
	<linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2] PM / Sleep: Timer quiesce in freeze state

On Thursday, October 30, 2014 10:58:23 AM Li, Aubrey wrote:
> The patch is based on v3.17, merged with Rafael's pm+acpi-3.18-rc1 tag from
> linux-pm.git tree.
> 
> The patch is based on the patch PeterZ initially wrote.
> ---
> Freeze is a general power saving state that processes are frozen, devices
> are suspended and CPUs are in idle state. However, when the system enters
> freeze state, there are a few timers keep ticking and hence consumes more
> power unnecessarily. The observed timer events in freeze state are:
> - tick_sched_timer
> - watchdog lockup detector
> - realtime scheduler period timer
> 
> The system power consumption in freeze state will be reduced significantly
> if we quiesce these timers.
> 
> On Baytrail-T(ASUS_T100) platform, when the system is freezed to low power
> idle state(S0ix), quiescing these timers saves 29.8% power(94.48mw -> 66.32mw).
> 
> The patch is also tested on:
> - Sandybrdige-EP system, both RTC alarm and power button are able to wake
>   the system up from freeze state.
> - HP laptop EliteBook 8460p, both RTC alarm and power button are able to
>   wake the system up from freeze state.
> 
> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Alan Cox <alan@...ux.intel.com>

Peter, Thomas, any comments here?

> ---
>  arch/x86/kernel/apic/apic.c        |   8 ++
>  drivers/cpuidle/cpuidle.c          |  12 +++
>  kernel/power/suspend.c             | 185 +++++++++++++++++++++++++++++++++++--
>  kernel/time/timekeeping.c          |   4 +-
>  kernel/time/timekeeping_internal.h |   3 +
>  5 files changed, 204 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 6776027..f2bb645 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -917,6 +917,14 @@ static void local_apic_timer_interrupt(void)
>  	 */
>  	inc_irq_stat(apic_timer_irqs);
>  
> +	/*
> +	 * if timekeeping is suspended, the clock event device will be
> +	 * suspended as well, so we are not supposed to invoke the event
> +	 * handler of clock event device.
> +	 */
> +	if (unlikely(timekeeping_suspended))
> +		return;
> +
>  	evt->event_handler(evt);
>  }
>  
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index ee9df5e..8f84f40 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -119,6 +119,18 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
>  	ktime_t time_start, time_end;
>  	s64 diff;
>  
> +	/*
> +	 * under the scenario of use deepest idle state, the timekeeping
> +	 * could be suspended as well as the clock source device, so we
> +	 * bypass the idle counter update for this case
> +	 */
> +	if (unlikely(use_deepest_state)) {
> +		entered_state = target_state->enter(dev, drv, index);
> +		if (!cpuidle_state_is_coupled(dev, drv, entered_state))
> +			local_irq_enable();
> +		return entered_state;
> +	}
> +
>  	trace_cpu_idle_rcuidle(index, dev->cpu);
>  	time_start = ktime_get();
>  
> diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> index 4ca9a33..660fd15 100644
> --- a/kernel/power/suspend.c
> +++ b/kernel/power/suspend.c
> @@ -28,16 +28,20 @@
>  #include <linux/ftrace.h>
>  #include <trace/events/power.h>
>  #include <linux/compiler.h>
> +#include <linux/stop_machine.h>
> +#include <linux/clockchips.h>
> +#include <linux/hrtimer.h>
>  
>  #include "power.h"
> +#include "../time/tick-internal.h"
> +#include "../time/timekeeping_internal.h"
>  
>  const char *pm_labels[] = { "mem", "standby", "freeze", NULL };
>  const char *pm_states[PM_SUSPEND_MAX];
>  
>  static const struct platform_suspend_ops *suspend_ops;
>  static const struct platform_freeze_ops *freeze_ops;
> -static DECLARE_WAIT_QUEUE_HEAD(suspend_freeze_wait_head);
> -static bool suspend_freeze_wake;
> +static int suspend_freeze_wake;
>  
>  void freeze_set_ops(const struct platform_freeze_ops *ops)
>  {
> @@ -48,22 +52,191 @@ void freeze_set_ops(const struct platform_freeze_ops *ops)
>  
>  static void freeze_begin(void)
>  {
> -	suspend_freeze_wake = false;
> +	suspend_freeze_wake = -1;
> +}
> +
> +enum freezer_state {
> +	FREEZER_NONE,
> +	FREEZER_PICK_TK,
> +	FREEZER_SUSPEND_CLKEVT,
> +	FREEZER_SUSPEND_TK,
> +	FREEZER_IDLE,
> +	FREEZER_RESUME_TK,
> +	FREEZER_RESUME_CLKEVT,
> +	FREEZER_EXIT,
> +};
> +
> +struct freezer_data {
> +	int			thread_num;
> +	atomic_t		thread_ack;
> +	enum freezer_state	state;
> +};
> +
> +static void set_state(struct freezer_data *fd, enum freezer_state state)
> +{
> +	/* set ack counter */
> +	atomic_set(&fd->thread_ack, fd->thread_num);
> +	/* guarantee the write ordering between ack counter and state */
> +	smp_wmb();
> +	fd->state = state;
> +}
> +
> +static void ack_state(struct freezer_data *fd)
> +{
> +	if (atomic_dec_and_test(&fd->thread_ack))
> +		set_state(fd, fd->state + 1);
> +}
> +
> +static void freezer_pick_tk(int cpu)
> +{
> +	if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) {
> +		static DEFINE_SPINLOCK(lock);
> +
> +		spin_lock(&lock);
> +		if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
> +			tick_do_timer_cpu = cpu;
> +		spin_unlock(&lock);
> +	}
> +}
> +
> +static void freezer_suspend_clkevt(int cpu)
> +{
> +	if (tick_do_timer_cpu == cpu)
> +		return;
> +
> +	clockevents_notify(CLOCK_EVT_NOTIFY_SUSPEND, NULL);
> +}
> +
> +static void freezer_suspend_tk(int cpu)
> +{
> +	if (tick_do_timer_cpu != cpu)
> +		return;
> +
> +	timekeeping_suspend();
> +
> +}
> +
> +static void freezer_idle(int cpu)
> +{
> +	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
> +	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> +
> +	stop_critical_timings();
> +
> +	while (suspend_freeze_wake == -1) {
> +		int next_state;
> +
> +		/*
> +		 * interrupt must be disabled before cpu enters idle
> +		 */
> +		local_irq_disable();
> +
> +		next_state = cpuidle_select(drv, dev);
> +		if (next_state < 0) {
> +			arch_cpu_idle();
> +			continue;
> +		}
> +		/*
> +		 * cpuidle_enter will return with interrupt enabled
> +		 */
> +		cpuidle_enter(drv, dev, next_state);
> +	}
> +
> +	if (suspend_freeze_wake == cpu)
> +		kick_all_cpus_sync();
> +
> +	/*
> +	 * We disable interrupt here for the rest of resume operations
> +	 */
> +	local_irq_disable();
> +	start_critical_timings();
> +}
> +
> +static void freezer_resume_tk(int cpu)
> +{
> +	if (tick_do_timer_cpu != cpu)
> +		return;
> +
> +	timekeeping_resume();
> +}
> +
> +static void freezer_resume_clkevt(int cpu)
> +{
> +	if (tick_do_timer_cpu == cpu) {
> +		/*
> +		 * Turn on the interrupt on the tick timer CPU as freezer
> +		 * tasks are finished.
> +		 */
> +		local_irq_enable();
> +		return;
> +	}
> +
> +	touch_softlockup_watchdog();
> +	clockevents_notify(CLOCK_EVT_NOTIFY_RESUME, NULL);
> +	hrtimers_resume();
> +	/*
> +	 * Turn on the interrupt on the non-tick-timer CPUs as freezer
> +	 * tasks are finished
> +	 */
> +	local_irq_enable();
> +}
> +
> +typedef void (*freezer_fn)(int);
> +
> +static freezer_fn freezer_func[FREEZER_EXIT] = {
> +	NULL,
> +	freezer_pick_tk,
> +	freezer_suspend_clkevt,
> +	freezer_suspend_tk,
> +	freezer_idle,
> +	freezer_resume_tk,
> +	freezer_resume_clkevt,
> +};
> +
> +static int freezer_stopper_fn(void *arg)
> +{
> +	struct freezer_data *fd = arg;
> +	enum freezer_state state = FREEZER_NONE;
> +	int cpu = smp_processor_id();
> +
> +	do {
> +		cpu_relax();
> +		if (fd->state != state) {
> +			state = fd->state;
> +			if (freezer_func[state])
> +				(*freezer_func[state])(cpu);
> +			ack_state(fd);
> +		}
> +	} while (fd->state != FREEZER_EXIT);
> +
> +	return 0;
>  }
>  
>  static void freeze_enter(void)
>  {
> +	struct freezer_data fd;
> +
>  	cpuidle_use_deepest_state(true);
>  	cpuidle_resume();
> -	wait_event(suspend_freeze_wait_head, suspend_freeze_wake);
> +
> +	get_online_cpus();
> +
> +	fd.thread_num = num_online_cpus();
> +	set_state(&fd, FREEZER_PICK_TK);
> +
> +	__stop_machine(freezer_stopper_fn, &fd, cpu_online_mask);
> +
> +	put_online_cpus();
> +
>  	cpuidle_pause();
>  	cpuidle_use_deepest_state(false);
>  }
>  
>  void freeze_wake(void)
>  {
> -	suspend_freeze_wake = true;
> -	wake_up(&suspend_freeze_wait_head);
> +	if (suspend_freeze_wake != -1)
> +		return;
> +	suspend_freeze_wake = smp_processor_id();
>  }
>  EXPORT_SYMBOL_GPL(freeze_wake);
>  
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index ec1791f..23d8feb 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1114,7 +1114,7 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
>   * xtime/wall_to_monotonic/jiffies/etc are
>   * still managed by arch specific suspend/resume code.
>   */
> -static void timekeeping_resume(void)
> +void timekeeping_resume(void)
>  {
>  	struct timekeeper *tk = &tk_core.timekeeper;
>  	struct clocksource *clock = tk->tkr.clock;
> @@ -1195,7 +1195,7 @@ static void timekeeping_resume(void)
>  	hrtimers_resume();
>  }
>  
> -static int timekeeping_suspend(void)
> +int timekeeping_suspend(void)
>  {
>  	struct timekeeper *tk = &tk_core.timekeeper;
>  	unsigned long flags;
> diff --git a/kernel/time/timekeeping_internal.h b/kernel/time/timekeeping_internal.h
> index 4ea005a..ed7a574 100644
> --- a/kernel/time/timekeeping_internal.h
> +++ b/kernel/time/timekeeping_internal.h
> @@ -26,4 +26,7 @@ static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
>  }
>  #endif
>  
> +extern int timekeeping_suspend(void);
> +extern void timekeeping_resume(void);
> +
>  #endif /* _TIMEKEEPING_INTERNAL_H */
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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