From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH v3]PM/Sleep: Timer quiesce in freeze state Date: Thu, 29 Jan 2015 23:20:10 +0100 Message-ID: <16564156.c5NBzjJuA3@vostro.rjw.lan> References: <54866625.8010406@linux.intel.com> <54C5FE6A.9010300@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from v094114.home.net.pl ([79.96.170.134]:52908 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753388AbbA2V5X (ORCPT ); Thu, 29 Jan 2015 16:57:23 -0500 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Thomas Gleixner Cc: "Li, Aubrey" , Peter Zijlstra , "Brown, Len" , Alan Cox , LKML , Linux PM list On Monday, January 26, 2015 10:40:24 AM Thomas Gleixner wrote: > On Mon, 26 Jan 2015, Li, Aubrey wrote: > > On 2015/1/22 18:15, Thomas Gleixner wrote: > > > Can we please stop adding more crap to that notifier thing? I rather > > > see that go away than being expanded. > > > > Are you referring to FREEZE_PREPARE or remove all of FREEZE staff at all? > > > > What's the disadvantage of adding more notifier? > > clockevents_notify() is not a notifier. Its a multiplex call and I > want to get rid of it and replace it with explicit functions. > > > >> + /* > > >> + * cpuidle_enter will return with interrupt enabled > > >> + */ > > >> + cpuidle_enter(drv, dev, next_state); > > > > > > How is that supposed to work? > > > > > > If timekeeping is not yet unfrozen, then any interrupt handling code > > > which calls anything time related is going to hit lala land. > > > > > > You must guarantee that timekeeping is unfrozen before any interrupt > > > is handled. If you cannot guarantee that, you cannot freeze > > > timekeeping ever. > > > > > > The cpu local tick device is less critical, but it happens to work by > > > chance, not by design. > > > > There are two way to guarantee this: the first way is, disable interrupt > > before timekeeping frozen and enable interrupt after timekeeping is > > unfrozen. However, we need to handle wakeup handler before unfreeze > > timekeeping to wake freeze task up from wait queue. > > > > So we have to go the other way, the other way is, we ignore time related > > calls during freeze, like what I added in irq_enter below. > > Groan. You just do not call in irq_enter/exit(), but what prevents any > interrupt handler or whatever to call into the time/timer code after > interrupts got reenabled? > > Nothing. > > > Or, we need to re-implement freeze wait and wake up mechanism? > > You need to make sure in the low level idle implementation that this > cannot happen. > > tick_freeze() > { > raw_spin_lock(&tick_freeze_lock); > tick_frozen++; > if (tick_frozen == num_online_cpus()) > timekeeping_suspend(); > else > tick_suspend_local(); > raw_spin_unlock(&tick_freeze_lock); > } > > tick_unfreeze() > { > raw_spin_lock(&tick_freeze_lock); > if (tick_frozen == num_online_cpus()) > timekeeping_resume(); > else > tick_resume_local(); > tick_frozen--; > raw_spin_unlock(&tick_freeze_lock); > } > > idle_freeze() > { > local_irq_disable(); > > tick_freeze(); > > /* Must keep interrupts disabled! */ > go_deep_idle() > > tick_unfreeze(); > > local_irq_enable(); > } > > That's the only way you can do it proper, everything else will just be > a horrible mess of bandaids and duct tape. > > So that does not need any of the irq_enter/exit conditionals, it does > not need the real_handler hack. It just works. > > The only remaining issue might be a NMI calling into > ktime_get_mono_fast_ns() before timekeeping is resumed. Its probably a > non issue on x86/tsc, but it might be a problem on other platforms > which turn off devices, clocks, It's not rocket science to prevent > that. So the patch below is my version of the $subject one trying to take the above suggestion into account. It doesn not address the ktime_get_mono_fast_ns() in NMI case at this stage, because quite frankly I'd prefer to get the core changes right in the first place. The new ->enter_freeze callback is there in struct cpuidle_state, because we generally cannot trust the existing ->enter callbacks to keep interrupts disabled all the time. Some of them enable interrupts temporarily and some idle entry methods enable interrupts automatically on exit. So ->enter_freeze is required to keep interrupts disabled and it is safe to suspend/resume timekeeping around it. The rest is reasonably straightforward. If suspend-to-idle is requested, couidle_idle_call() calls cpuidle_enter_freeze() that bypasses the governor and selects the deepest suitable state. If ->enter_freeze is available, it will be used along with tick_freeze()/tick_unfreeze() and the normal idle entry code path will be used otherwise. I'm not quite sure if rcu_idle_enter/exit() needs to be done around that. The reason why it isn't in the current patch is because timekeeping_resume() was very unhappy about being part of the extended grace period and complained about that very loudly. Which of course means that the patch has been tested (lightly, with a hacked ACPI cpuidle driver) and that's why it still uses tick_suspend_broadcast() in tick_freeze(). Please let me know what you think. Rafael --- drivers/cpuidle/cpuidle.c | 83 +++++++++++++++++++++++++++++++--------------- include/linux/cpuidle.h | 8 +++- include/linux/suspend.h | 2 + include/linux/tick.h | 2 + kernel/power/suspend.c | 37 ++++++++++++++++---- kernel/sched/idle.c | 9 ++++ kernel/time/tick-common.c | 50 +++++++++++++++++++++++++++ kernel/time/timekeeping.c | 4 +- kernel/time/timekeeping.h | 2 + 9 files changed, 160 insertions(+), 37 deletions(-) Index: linux-pm/kernel/power/suspend.c =================================================================== --- linux-pm.orig/kernel/power/suspend.c +++ linux-pm/kernel/power/suspend.c @@ -37,7 +37,20 @@ 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; + +/* Suspend-to-idle state machnine. */ +enum freeze_state { + FREEZE_STATE_NONE, /* Not suspended/suspending. */ + FREEZE_STATE_ENTER, /* Enter suspend-to-idle. */ + FREEZE_STATE_WAKE, /* Wake up from suspend-to-idle. */ +}; + +static enum freeze_state suspend_freeze_state; + +bool idle_should_freeze(void) +{ + return suspend_freeze_state == FREEZE_STATE_ENTER; +} void freeze_set_ops(const struct platform_freeze_ops *ops) { @@ -48,22 +61,32 @@ void freeze_set_ops(const struct platfor static void freeze_begin(void) { - suspend_freeze_wake = false; + suspend_freeze_state = FREEZE_STATE_NONE; } static void freeze_enter(void) { - cpuidle_use_deepest_state(true); + suspend_freeze_state = FREEZE_STATE_ENTER; + get_online_cpus(); cpuidle_resume(); - wait_event(suspend_freeze_wait_head, suspend_freeze_wake); + /* Push all the CPUs into the idle loop. */ + wake_up_all_idle_cpus(); + pr_debug("PM: suspend-to-idle\n"); + /* Make the current CPU wait so it can enter the idle loop too. */ + wait_event(suspend_freeze_wait_head, + suspend_freeze_state == FREEZE_STATE_WAKE); + pr_debug("PM: resume from suspend-to-idle\n"); cpuidle_pause(); - cpuidle_use_deepest_state(false); + put_online_cpus(); + suspend_freeze_state = FREEZE_STATE_NONE; } void freeze_wake(void) { - suspend_freeze_wake = true; - wake_up(&suspend_freeze_wait_head); + if (suspend_freeze_state > FREEZE_STATE_NONE) { + suspend_freeze_state = FREEZE_STATE_WAKE; + wake_up(&suspend_freeze_wait_head); + } } EXPORT_SYMBOL_GPL(freeze_wake); Index: linux-pm/include/linux/suspend.h =================================================================== --- linux-pm.orig/include/linux/suspend.h +++ linux-pm/include/linux/suspend.h @@ -203,6 +203,7 @@ extern void suspend_set_ops(const struct extern int suspend_valid_only_mem(suspend_state_t state); extern void freeze_set_ops(const struct platform_freeze_ops *ops); extern void freeze_wake(void); +extern bool idle_should_freeze(void); /** * arch_suspend_disable_irqs - disable IRQs for suspend @@ -230,6 +231,7 @@ static inline void suspend_set_ops(const static inline int pm_suspend(suspend_state_t state) { return -ENOSYS; } static inline void freeze_set_ops(const struct platform_freeze_ops *ops) {} static inline void freeze_wake(void) {} +static inline bool idle_should_freeze(void) { return false; } #endif /* !CONFIG_SUSPEND */ /* struct pbe is used for creating lists of pages that should be restored Index: linux-pm/kernel/sched/idle.c =================================================================== --- linux-pm.orig/kernel/sched/idle.c +++ linux-pm/kernel/sched/idle.c @@ -7,6 +7,7 @@ #include #include #include +#include #include @@ -96,6 +97,13 @@ static void cpuidle_idle_call(void) */ stop_critical_timings(); + if (idle_should_freeze()) { + cpuidle_enter_freeze(); + local_irq_enable(); + start_critical_timings(); + return; + } + /* * Tell the RCU framework we are entering an idle section, * so no more rcu read side critical sections and one more @@ -220,6 +228,7 @@ static void cpu_idle_loop(void) * know that the IPI is going to arrive right * away */ + if (cpu_idle_force_poll || tick_check_broadcast_expired()) cpu_idle_poll(); else Index: linux-pm/drivers/cpuidle/cpuidle.c =================================================================== --- linux-pm.orig/drivers/cpuidle/cpuidle.c +++ linux-pm/drivers/cpuidle/cpuidle.c @@ -19,6 +19,8 @@ #include #include #include +#include +#include #include #include "cpuidle.h" @@ -32,7 +34,6 @@ LIST_HEAD(cpuidle_detected_devices); static int enabled_devices; static int off __read_mostly; static int initialized __read_mostly; -static bool use_deepest_state __read_mostly; int cpuidle_disabled(void) { @@ -66,36 +67,23 @@ int cpuidle_play_dead(void) } /** - * cpuidle_use_deepest_state - Enable/disable the "deepest idle" mode. - * @enable: Whether enable or disable the feature. - * - * If the "deepest idle" mode is enabled, cpuidle will ignore the governor and - * always use the state with the greatest exit latency (out of the states that - * are not disabled). - * - * This function can only be called after cpuidle_pause() to avoid races. - */ -void cpuidle_use_deepest_state(bool enable) -{ - use_deepest_state = enable; -} - -/** - * cpuidle_find_deepest_state - Find the state of the greatest exit latency. - * @drv: cpuidle driver for a given CPU. - * @dev: cpuidle device for a given CPU. + * cpuidle_find_deepest_state - Find deepest state meeting specific conditions. + * @drv: cpuidle driver for the given CPU. + * @dev: cpuidle device for the given CPU. + * @freeze: Whether or not the state should be suitable for suspend-to-idle. */ static int cpuidle_find_deepest_state(struct cpuidle_driver *drv, - struct cpuidle_device *dev) + struct cpuidle_device *dev, bool freeze) { unsigned int latency_req = 0; - int i, ret = CPUIDLE_DRIVER_STATE_START - 1; + int i, ret = freeze ? -1 : CPUIDLE_DRIVER_STATE_START - 1; for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) { struct cpuidle_state *s = &drv->states[i]; struct cpuidle_state_usage *su = &dev->states_usage[i]; - if (s->disabled || su->disable || s->exit_latency <= latency_req) + if (s->disabled || su->disable || s->exit_latency <= latency_req + || (freeze && !s->enter_freeze)) continue; latency_req = s->exit_latency; @@ -104,6 +92,52 @@ static int cpuidle_find_deepest_state(st return ret; } +static void enter_freeze_proper(struct cpuidle_driver *drv, + struct cpuidle_device *dev, int index) +{ + tick_freeze(); + drv->states[index].enter_freeze(dev, drv, index); + tick_unfreeze(); +} + +/** + * cpuidle_enter_freeze - Enter an idle state suitable for suspend-to-idle. + * + * If there are states with the ->enter_freeze callback, find the deepest of + * them and enter it with frozen tick. Otherwise, find the deepest state + * available and enter it normally. + */ +void cpuidle_enter_freeze(void) +{ + struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices); + struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); + int index; + + /* + * Find the deepest state with ->enter_freeze present, which guarantees + * that interrupts won't be enabled when it exits and allows the tick to + * be frozen safely. + */ + index = cpuidle_find_deepest_state(drv, dev, true); + if (index >= 0) { + enter_freeze_proper(drv, dev, index); + return; + } + + /* + * It is not safe to freeze the tick, find the deepest state available + * at all and try to enter it normally. + */ + index = cpuidle_find_deepest_state(drv, dev, false); + if (index >= 0) + cpuidle_enter(drv, dev, index); + else + arch_cpu_idle(); + + /* Interrupts are enabled again here. */ + local_irq_disable(); +} + /** * cpuidle_enter_state - enter the state and update stats * @dev: cpuidle device for this cpu @@ -166,9 +200,6 @@ int cpuidle_select(struct cpuidle_driver if (!drv || !dev || !dev->enabled) return -EBUSY; - if (unlikely(use_deepest_state)) - return cpuidle_find_deepest_state(drv, dev); - return cpuidle_curr_governor->select(drv, dev); } @@ -200,7 +231,7 @@ int cpuidle_enter(struct cpuidle_driver */ void cpuidle_reflect(struct cpuidle_device *dev, int index) { - if (cpuidle_curr_governor->reflect && !unlikely(use_deepest_state)) + if (cpuidle_curr_governor->reflect) cpuidle_curr_governor->reflect(dev, index); } Index: linux-pm/include/linux/cpuidle.h =================================================================== --- linux-pm.orig/include/linux/cpuidle.h +++ linux-pm/include/linux/cpuidle.h @@ -50,6 +50,10 @@ struct cpuidle_state { int index); int (*enter_dead) (struct cpuidle_device *dev, int index); + + void (*enter_freeze) (struct cpuidle_device *dev, + struct cpuidle_driver *drv, + int index); }; /* Idle State Flags */ @@ -141,7 +145,7 @@ extern void cpuidle_resume(void); extern int cpuidle_enable_device(struct cpuidle_device *dev); extern void cpuidle_disable_device(struct cpuidle_device *dev); extern int cpuidle_play_dead(void); -extern void cpuidle_use_deepest_state(bool enable); +extern void cpuidle_enter_freeze(void); extern struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev); #else @@ -174,7 +178,7 @@ static inline int cpuidle_enable_device( {return -ENODEV; } static inline void cpuidle_disable_device(struct cpuidle_device *dev) { } static inline int cpuidle_play_dead(void) {return -ENODEV; } -static inline void cpuidle_use_deepest_state(bool enable) {} +static inline void cpuidle_enter_freeze(void) { } static inline struct cpuidle_driver *cpuidle_get_cpu_driver( struct cpuidle_device *dev) {return NULL; } #endif Index: linux-pm/kernel/time/tick-common.c =================================================================== --- linux-pm.orig/kernel/time/tick-common.c +++ linux-pm/kernel/time/tick-common.c @@ -394,6 +394,56 @@ void tick_resume(void) } } +static DEFINE_RAW_SPINLOCK(tick_freeze_lock); +static unsigned int tick_freeze_depth; + +/** + * tick_freeze - Suspend the local tick and (possibly) timekeeping. + * + * Check if this is the last online CPU executing the function and if so, + * suspend timekeeping. Otherwise suspend the local tick. + * + * Call with interrupts disabled. Must be balanced with %tick_unfreeze(). + * Interrupts must not be enabled before the subsequent %tick_unfreeze(). + */ +void tick_freeze(void) +{ + raw_spin_lock(&tick_freeze_lock); + + tick_freeze_depth++; + if (tick_freeze_depth == num_online_cpus()) { + timekeeping_suspend(); + } else { + tick_suspend(); + tick_suspend_broadcast(); + } + + raw_spin_unlock(&tick_freeze_lock); +} + +/** + * tick_unfreeze - Resume the local tick and (possibly) timekeeping. + * + * Check if this is the first CPU executing the function and if so, resume + * timekeeping. Otherwise resume the local tick. + * + * Call with interrupts disabled. Must be balanced with %tick_freeze(). + * Interrupts must not be enabled after the preceding %tick_freeze(). + */ +void tick_unfreeze(void) +{ + raw_spin_lock(&tick_freeze_lock); + + if (tick_freeze_depth == num_online_cpus()) + timekeeping_resume(); + else + tick_resume(); + + tick_freeze_depth--; + + raw_spin_unlock(&tick_freeze_lock); +} + /** * tick_init - initialize the tick control */ Index: linux-pm/include/linux/tick.h =================================================================== --- linux-pm.orig/include/linux/tick.h +++ linux-pm/include/linux/tick.h @@ -226,5 +226,7 @@ static inline void tick_nohz_task_switch __tick_nohz_task_switch(tsk); } +extern void tick_freeze(void); +extern void tick_unfreeze(void); #endif Index: linux-pm/kernel/time/timekeeping.c =================================================================== --- linux-pm.orig/kernel/time/timekeeping.c +++ linux-pm/kernel/time/timekeeping.c @@ -1170,7 +1170,7 @@ void timekeeping_inject_sleeptime64(stru * 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; @@ -1251,7 +1251,7 @@ 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; Index: linux-pm/kernel/time/timekeeping.h =================================================================== --- linux-pm.orig/kernel/time/timekeeping.h +++ linux-pm/kernel/time/timekeeping.h @@ -16,5 +16,7 @@ extern int timekeeping_inject_offset(str extern s32 timekeeping_get_tai_offset(void); extern void timekeeping_set_tai_offset(s32 tai_offset); extern void timekeeping_clocktai(struct timespec *ts); +extern int timekeeping_suspend(void); +extern void timekeeping_resume(void); #endif