From 8234f6734c5d74ac794e5517437f51c57d65f865 Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Fri, 14 Dec 2018 15:22:25 +0100 Subject: PM-runtime: Switch autosuspend over to using hrtimers PM-runtime uses the timer infrastructure for autosuspend. This implies that the minimum time before autosuspending a device is in the range of 1 tick included to 2 ticks excluded -On arm64 this means between 4ms and 8ms with default jiffies configuration -And on arm, it is between 10ms and 20ms These values are quite high for embedded systems which sometimes want the duration to be in the range of 1 ms. It is possible to switch autosuspend over to using hrtimers to get finer granularity for short durations and take advantage of slack to retain some margins and get long timeouts with minimum wakeups. On an arm64 platform that uses 1ms for autosuspending timeout of its GPU, idle power is reduced by 10% with hrtimer. The latency impact on arm64 hikey octo cores is: - mark_last_busy: from 1.11 us to 1.25 us - rpm_suspend: from 15.54 us to 15.38 us [Only the code path of rpm_suspend() that starts hrtimer has been measured.] arm64 image (arm64 default defconfig) decreases by around 3KB with following details: $ size vmlinux-timer text data bss dec hex filename 12034646 6869268 386840 19290754 1265a82 vmlinux $ size vmlinux-hrtimer text data bss dec hex filename 12030550 6870164 387032 19287746 1264ec2 vmlinux The latency impact on arm 32bits snowball dual cores is : - mark_last_busy: from 0.31 us usec to 0.77 us - rpm_suspend: from 6.83 us to 6.67 usec The increase of the image for snowball platform that I used for testing performance impact, is neglictable (244B). $ size vmlinux-timer text data bss dec hex filename 7157961 2119580 264120 9541661 91981d build-ux500/vmlinux size vmlinux-hrtimer text data bss dec hex filename 7157773 2119884 264248 9541905 919911 vmlinux-hrtimer And arm 32bits image (multi_v7_defconfig) increases by around 1.7KB with following details: $ size vmlinux-timer text data bss dec hex filename 13304443 6803420 402768 20510631 138f7a7 vmlinux $ size vmlinux-hrtimer text data bss dec hex filename 13304299 6805276 402768 20512343 138fe57 vmlinux Signed-off-by: Vincent Guittot Reviewed-by: Ulf Hansson Signed-off-by: Rafael J. Wysocki --- include/linux/pm_runtime.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux/pm_runtime.h') diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h index f0fc4700b6ff..54af4eef169f 100644 --- a/include/linux/pm_runtime.h +++ b/include/linux/pm_runtime.h @@ -51,7 +51,7 @@ extern void pm_runtime_no_callbacks(struct device *dev); extern void pm_runtime_irq_safe(struct device *dev); extern void __pm_runtime_use_autosuspend(struct device *dev, bool use); extern void pm_runtime_set_autosuspend_delay(struct device *dev, int delay); -extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev); +extern u64 pm_runtime_autosuspend_expiration(struct device *dev); extern void pm_runtime_update_max_time_suspended(struct device *dev, s64 delta_ns); extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable); @@ -105,7 +105,7 @@ static inline bool pm_runtime_callbacks_present(struct device *dev) static inline void pm_runtime_mark_last_busy(struct device *dev) { - WRITE_ONCE(dev->power.last_busy, jiffies); + WRITE_ONCE(dev->power.last_busy, ktime_to_ns(ktime_get())); } static inline bool pm_runtime_is_irq_safe(struct device *dev) @@ -168,7 +168,7 @@ static inline void __pm_runtime_use_autosuspend(struct device *dev, bool use) {} static inline void pm_runtime_set_autosuspend_delay(struct device *dev, int delay) {} -static inline unsigned long pm_runtime_autosuspend_expiration( +static inline u64 pm_runtime_autosuspend_expiration( struct device *dev) { return 0; } static inline void pm_runtime_set_memalloc_noio(struct device *dev, bool enable){} -- cgit v1.2.3 From 15efb47dc560849d0c07db96fdad5121f2cf736e Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Wed, 30 Jan 2019 18:26:02 +0100 Subject: PM-runtime: Fix deadlock with ktime_get() A deadlock has been seen when swicthing clocksources which use PM-runtime. The call path is: change_clocksource ... write_seqcount_begin ... timekeeping_update ... sh_cmt_clocksource_enable ... rpm_resume pm_runtime_mark_last_busy ktime_get do read_seqcount_begin while read_seqcount_retry .... write_seqcount_end Although we should be safe because we haven't yet changed the clocksource at that time, we can't do that because of seqcount protection. Use ktime_get_mono_fast_ns() instead which is lock safe for such cases. With ktime_get_mono_fast_ns, the timestamp is not guaranteed to be monotonic across an update and as a result can goes backward. According to update_fast_timekeeper() description: "In the worst case, this can result is a slightly wrong timestamp (a few nanoseconds)". For PM-runtime autosuspend, this means only that the suspend decision may be slightly suboptimal. Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using hrtimers") Reported-by: Biju Das Signed-off-by: Vincent Guittot Reviewed-by: Ulf Hansson Signed-off-by: Rafael J. Wysocki --- drivers/base/power/runtime.c | 10 +++++----- include/linux/pm_runtime.h | 2 +- 2 files changed, 6 insertions(+), 6 deletions(-) (limited to 'include/linux/pm_runtime.h') diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c index 457be03b744d..0ea2139c50d8 100644 --- a/drivers/base/power/runtime.c +++ b/drivers/base/power/runtime.c @@ -130,7 +130,7 @@ u64 pm_runtime_autosuspend_expiration(struct device *dev) { int autosuspend_delay; u64 last_busy, expires = 0; - u64 now = ktime_to_ns(ktime_get()); + u64 now = ktime_get_mono_fast_ns(); if (!dev->power.use_autosuspend) goto out; @@ -909,7 +909,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer) * If 'expires' is after the current time, we've been called * too early. */ - if (expires > 0 && expires < ktime_to_ns(ktime_get())) { + if (expires > 0 && expires < ktime_get_mono_fast_ns()) { dev->power.timer_expires = 0; rpm_suspend(dev, dev->power.timer_autosuspends ? (RPM_ASYNC | RPM_AUTO) : RPM_ASYNC); @@ -928,7 +928,7 @@ static enum hrtimer_restart pm_suspend_timer_fn(struct hrtimer *timer) int pm_schedule_suspend(struct device *dev, unsigned int delay) { unsigned long flags; - ktime_t expires; + u64 expires; int retval; spin_lock_irqsave(&dev->power.lock, flags); @@ -945,8 +945,8 @@ int pm_schedule_suspend(struct device *dev, unsigned int delay) /* Other scheduled or pending requests need to be canceled. */ pm_runtime_cancel_pending(dev); - expires = ktime_add(ktime_get(), ms_to_ktime(delay)); - dev->power.timer_expires = ktime_to_ns(expires); + expires = ktime_get_mono_fast_ns() + (u64)delay * NSEC_PER_MSEC; + dev->power.timer_expires = expires; dev->power.timer_autosuspends = 0; hrtimer_start(&dev->power.suspend_timer, expires, HRTIMER_MODE_ABS); diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h index 54af4eef169f..fed5be706bc9 100644 --- a/include/linux/pm_runtime.h +++ b/include/linux/pm_runtime.h @@ -105,7 +105,7 @@ static inline bool pm_runtime_callbacks_present(struct device *dev) static inline void pm_runtime_mark_last_busy(struct device *dev) { - WRITE_ONCE(dev->power.last_busy, ktime_to_ns(ktime_get())); + WRITE_ONCE(dev->power.last_busy, ktime_get_mono_fast_ns()); } static inline bool pm_runtime_is_irq_safe(struct device *dev) -- cgit v1.2.3