124cf9117c
The efficiency of suspend-to-idle depends on being able to keep CPUs in the deepest available idle states for as much time as possible. Ideally, they should only be brought out of idle by system wakeup interrupts. However, timer interrupts occurring periodically prevent that from happening and it is not practical to chase all of the "misbehaving" timers in a whack-a-mole fashion. A much more effective approach is to suspend the local ticks for all CPUs and the entire timekeeping along the lines of what is done during full suspend, which also helps to keep suspend-to-idle and full suspend reasonably similar. The idea is to suspend the local tick on each CPU executing cpuidle_enter_freeze() and to make the last of them suspend the entire timekeeping. That should prevent timer interrupts from triggering until an IO interrupt wakes up one of the CPUs. It needs to be done with interrupts disabled on all of the CPUs, though, because otherwise the suspended clocksource might be accessed by an interrupt handler which might lead to fatal consequences. Unfortunately, the existing ->enter callbacks provided by cpuidle drivers generally cannot be used for implementing that, because some of them re-enable interrupts temporarily and some idle entry methods cause interrupts to be re-enabled automatically on exit. Also some of these callbacks manipulate local clock event devices of the CPUs which really shouldn't be done after suspending their ticks. To overcome that difficulty, introduce a new cpuidle state callback, ->enter_freeze, that will be guaranteed (1) to keep interrupts disabled all the time (and return with interrupts disabled) and (2) not to touch the CPU timer devices. Modify cpuidle_enter_freeze() to look for the deepest available idle state with ->enter_freeze present and to make the CPU execute that callback with suspended tick (and the last of the online CPUs to execute it with suspended timekeeping). Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
23 lines
739 B
C
23 lines
739 B
C
#ifndef _KERNEL_TIME_TIMEKEEPING_H
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#define _KERNEL_TIME_TIMEKEEPING_H
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/*
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* Internal interfaces for kernel/time/
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*/
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extern ktime_t ktime_get_update_offsets_tick(ktime_t *offs_real,
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ktime_t *offs_boot,
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ktime_t *offs_tai);
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extern ktime_t ktime_get_update_offsets_now(ktime_t *offs_real,
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ktime_t *offs_boot,
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ktime_t *offs_tai);
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extern int timekeeping_valid_for_hres(void);
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extern u64 timekeeping_max_deferment(void);
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extern int timekeeping_inject_offset(struct timespec *ts);
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extern s32 timekeeping_get_tai_offset(void);
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extern void timekeeping_set_tai_offset(s32 tai_offset);
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extern void timekeeping_clocktai(struct timespec *ts);
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extern int timekeeping_suspend(void);
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extern void timekeeping_resume(void);
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#endif
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