From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> Prepare the scheduler tick code for reworking the idle loop to avoid stopping the tick in some cases.
Move away the tick_nohz_start_idle() invocation from __tick_nohz_idle_enter(), rename the latter to __tick_nohz_idle_stop_tick() and define tick_nohz_idle_stop_tick() as a wrapper around it for calling it from the outside. Make tick_nohz_idle_enter() only call tick_nohz_start_idle() instead of calling the entire __tick_nohz_idle_enter(), add another wrapper disabling and enabling interrupts around tick_nohz_idle_stop_tick() and make the current callers of tick_nohz_idle_enter() call it too to retain their current functionality. Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> --- arch/x86/xen/smp_pv.c | 1 + include/linux/tick.h | 9 +++++++++ kernel/sched/idle.c | 1 + kernel/time/tick-sched.c | 46 +++++++++++++++++++++++++--------------------- 4 files changed, 36 insertions(+), 21 deletions(-) Index: linux-pm/include/linux/tick.h =================================================================== --- linux-pm.orig/include/linux/tick.h +++ linux-pm/include/linux/tick.h @@ -114,6 +114,7 @@ enum tick_dep_bits { #ifdef CONFIG_NO_HZ_COMMON extern bool tick_nohz_enabled; extern int tick_nohz_tick_stopped(void); +extern void tick_nohz_idle_stop_tick(void); extern void tick_nohz_idle_enter(void); extern void tick_nohz_idle_exit(void); extern void tick_nohz_irq_exit(void); @@ -125,6 +126,7 @@ extern u64 get_cpu_iowait_time_us(int cp #else /* !CONFIG_NO_HZ_COMMON */ #define tick_nohz_enabled (0) static inline int tick_nohz_tick_stopped(void) { return 0; } +static inline void tick_nohz_idle_stop_tick(void) { } static inline void tick_nohz_idle_enter(void) { } static inline void tick_nohz_idle_exit(void) { } @@ -136,6 +138,13 @@ static inline u64 get_cpu_idle_time_us(i static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } #endif /* !CONFIG_NO_HZ_COMMON */ +static inline void tick_nohz_idle_stop_tick_protected(void) +{ + local_irq_disable(); + tick_nohz_idle_stop_tick(); + local_irq_enable(); +} + #ifdef CONFIG_NO_HZ_FULL extern bool tick_nohz_full_running; extern cpumask_var_t tick_nohz_full_mask; Index: linux-pm/kernel/time/tick-sched.c =================================================================== --- linux-pm.orig/kernel/time/tick-sched.c +++ linux-pm/kernel/time/tick-sched.c @@ -539,14 +539,11 @@ static void tick_nohz_stop_idle(struct t sched_clock_idle_wakeup_event(); } -static ktime_t tick_nohz_start_idle(struct tick_sched *ts) +static void tick_nohz_start_idle(struct tick_sched *ts) { - ktime_t now = ktime_get(); - - ts->idle_entrytime = now; + ts->idle_entrytime = ktime_get(); ts->idle_active = 1; sched_clock_idle_sleep_event(); - return now; } /** @@ -911,19 +908,21 @@ static bool can_stop_idle_tick(int cpu, return true; } -static void __tick_nohz_idle_enter(struct tick_sched *ts) +static void __tick_nohz_idle_stop_tick(struct tick_sched *ts) { - ktime_t now, expires; + ktime_t expires; int cpu = smp_processor_id(); - now = tick_nohz_start_idle(ts); - if (can_stop_idle_tick(cpu, ts)) { int was_stopped = ts->tick_stopped; ts->idle_calls++; - expires = tick_nohz_stop_sched_tick(ts, now, cpu); + /* + * The idle entry time should be a sufficient approximation of + * the current time at this point. + */ + expires = tick_nohz_stop_sched_tick(ts, ts->idle_entrytime, cpu); if (expires > 0LL) { ts->idle_sleeps++; ts->idle_expires = expires; @@ -937,16 +936,19 @@ static void __tick_nohz_idle_enter(struc } /** - * tick_nohz_idle_enter - stop the idle tick from the idle task + * tick_nohz_idle_stop_tick - stop the idle tick from the idle task * * When the next event is more than a tick into the future, stop the idle tick - * Called when we start the idle loop. - * - * The arch is responsible of calling: + */ +void tick_nohz_idle_stop_tick(void) +{ + __tick_nohz_idle_stop_tick(this_cpu_ptr(&tick_cpu_sched)); +} + +/** + * tick_nohz_idle_enter - prepare for entering idle on the current CPU * - * - rcu_idle_enter() after its last use of RCU before the CPU is put - * to sleep. - * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. + * Called when we start the idle loop. */ void tick_nohz_idle_enter(void) { @@ -965,7 +967,7 @@ void tick_nohz_idle_enter(void) ts = this_cpu_ptr(&tick_cpu_sched); ts->inidle = 1; - __tick_nohz_idle_enter(ts); + tick_nohz_start_idle(ts); local_irq_enable(); } @@ -982,10 +984,12 @@ void tick_nohz_irq_exit(void) { struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); - if (ts->inidle) - __tick_nohz_idle_enter(ts); - else + if (ts->inidle) { + tick_nohz_start_idle(ts); + __tick_nohz_idle_stop_tick(ts); + } else { tick_nohz_full_update_tick(ts); + } } /** Index: linux-pm/arch/x86/xen/smp_pv.c =================================================================== --- linux-pm.orig/arch/x86/xen/smp_pv.c +++ linux-pm/arch/x86/xen/smp_pv.c @@ -425,6 +425,7 @@ static void xen_pv_play_dead(void) /* us * data back is to call: */ tick_nohz_idle_enter(); + tick_nohz_idle_stop_tick_protected(); cpuhp_online_idle(CPUHP_AP_ONLINE_IDLE); } Index: linux-pm/kernel/sched/idle.c =================================================================== --- linux-pm.orig/kernel/sched/idle.c +++ linux-pm/kernel/sched/idle.c @@ -221,6 +221,7 @@ static void do_idle(void) __current_set_polling(); tick_nohz_idle_enter(); + tick_nohz_idle_stop_tick_protected(); while (!need_resched()) { check_pgt_cache();