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![Frederic Weisbecker](/assets/img/avatar_default.png)
Reading idle/IO sleep time (eg: from /proc/stat) can race with idle exit updates because the state machine handling the stats is not atomic and requires a coherent read batch. As a result reading the sleep time may report irrelevant or backward values. Fix this with protecting the simple state machine within a seqcount. This is expected to be cheap enough not to add measurable performance impact on the idle path. Note this only fixes reader VS writer condition partitially. A race remains that involves remote updates of the CPU iowait task counter. It can hardly be fixed. Reported-by: Yu Liao <liaoyu15@huawei.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20230222144649.624380-4-frederic@kernel.org
122 lines
3.9 KiB
C
122 lines
3.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _TICK_SCHED_H
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#define _TICK_SCHED_H
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#include <linux/hrtimer.h>
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enum tick_device_mode {
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TICKDEV_MODE_PERIODIC,
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TICKDEV_MODE_ONESHOT,
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};
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struct tick_device {
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struct clock_event_device *evtdev;
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enum tick_device_mode mode;
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};
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enum tick_nohz_mode {
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NOHZ_MODE_INACTIVE,
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NOHZ_MODE_LOWRES,
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NOHZ_MODE_HIGHRES,
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};
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/**
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* struct tick_sched - sched tick emulation and no idle tick control/stats
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*
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* @inidle: Indicator that the CPU is in the tick idle mode
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* @tick_stopped: Indicator that the idle tick has been stopped
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* @idle_active: Indicator that the CPU is actively in the tick idle mode;
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* it is reset during irq handling phases.
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* @do_timer_last: CPU was the last one doing do_timer before going idle
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* @got_idle_tick: Tick timer function has run with @inidle set
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* @stalled_jiffies: Number of stalled jiffies detected across ticks
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* @last_tick_jiffies: Value of jiffies seen on last tick
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* @sched_timer: hrtimer to schedule the periodic tick in high
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* resolution mode
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* @last_tick: Store the last tick expiry time when the tick
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* timer is modified for nohz sleeps. This is necessary
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* to resume the tick timer operation in the timeline
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* when the CPU returns from nohz sleep.
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* @next_tick: Next tick to be fired when in dynticks mode.
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* @idle_jiffies: jiffies at the entry to idle for idle time accounting
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* @idle_waketime: Time when the idle was interrupted
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* @idle_entrytime: Time when the idle call was entered
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* @nohz_mode: Mode - one state of tick_nohz_mode
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* @last_jiffies: Base jiffies snapshot when next event was last computed
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* @timer_expires_base: Base time clock monotonic for @timer_expires
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* @timer_expires: Anticipated timer expiration time (in case sched tick is stopped)
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* @next_timer: Expiry time of next expiring timer for debugging purpose only
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* @idle_expires: Next tick in idle, for debugging purpose only
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* @idle_calls: Total number of idle calls
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* @idle_sleeps: Number of idle calls, where the sched tick was stopped
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* @idle_exittime: Time when the idle state was left
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* @idle_sleeptime: Sum of the time slept in idle with sched tick stopped
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* @iowait_sleeptime: Sum of the time slept in idle with sched tick stopped, with IO outstanding
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* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
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* @check_clocks: Notification mechanism about clocksource changes
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*/
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struct tick_sched {
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/* Common flags */
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unsigned int inidle : 1;
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unsigned int tick_stopped : 1;
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unsigned int idle_active : 1;
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unsigned int do_timer_last : 1;
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unsigned int got_idle_tick : 1;
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/* Tick handling: jiffies stall check */
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unsigned int stalled_jiffies;
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unsigned long last_tick_jiffies;
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/* Tick handling */
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struct hrtimer sched_timer;
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ktime_t last_tick;
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ktime_t next_tick;
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unsigned long idle_jiffies;
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ktime_t idle_waketime;
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/* Idle entry */
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seqcount_t idle_sleeptime_seq;
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ktime_t idle_entrytime;
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/* Tick stop */
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enum tick_nohz_mode nohz_mode;
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unsigned long last_jiffies;
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u64 timer_expires_base;
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u64 timer_expires;
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u64 next_timer;
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ktime_t idle_expires;
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unsigned long idle_calls;
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unsigned long idle_sleeps;
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/* Idle exit */
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ktime_t idle_exittime;
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ktime_t idle_sleeptime;
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ktime_t iowait_sleeptime;
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/* Full dynticks handling */
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atomic_t tick_dep_mask;
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/* Clocksource changes */
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unsigned long check_clocks;
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};
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extern struct tick_sched *tick_get_tick_sched(int cpu);
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extern void tick_setup_sched_timer(void);
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#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
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extern void tick_cancel_sched_timer(int cpu);
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#else
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static inline void tick_cancel_sched_timer(int cpu) { }
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#endif
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#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
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extern int __tick_broadcast_oneshot_control(enum tick_broadcast_state state);
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#else
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static inline int
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__tick_broadcast_oneshot_control(enum tick_broadcast_state state)
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{
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return -EBUSY;
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}
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#endif
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#endif
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