diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h index b5003856fd60..c924bb2498db 100644 --- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -31,6 +31,13 @@ * soft irq context * HRTIMER_MODE_HARD - Timer callback function will be executed in * hard irq context even on PREEMPT_RT. + * HRTIMER_MODE_LAZY_REARM - Avoid reprogramming if the timer was the + * first expiring timer and is moved into the + * future. Special mode for the HRTICK timer to + * avoid extensive reprogramming of the hardware, + * which is expensive in virtual machines. Risks + * a pointless expiry, but that's better than + * reprogramming on every context switch, */ enum hrtimer_mode { HRTIMER_MODE_ABS = 0x00, @@ -38,6 +45,7 @@ enum hrtimer_mode { HRTIMER_MODE_PINNED = 0x02, HRTIMER_MODE_SOFT = 0x04, HRTIMER_MODE_HARD = 0x08, + HRTIMER_MODE_LAZY_REARM = 0x10, HRTIMER_MODE_ABS_PINNED = HRTIMER_MODE_ABS | HRTIMER_MODE_PINNED, HRTIMER_MODE_REL_PINNED = HRTIMER_MODE_REL | HRTIMER_MODE_PINNED, diff --git a/include/linux/hrtimer_types.h b/include/linux/hrtimer_types.h index 8fbbb6bdf7a1..64381c64cdbd 100644 --- a/include/linux/hrtimer_types.h +++ b/include/linux/hrtimer_types.h @@ -33,6 +33,8 @@ enum hrtimer_restart { * @is_soft: Set if hrtimer will be expired in soft interrupt context. * @is_hard: Set if hrtimer will be expired in hard interrupt context * even on RT. + * @is_lazy: Set if the timer is frequently rearmed to avoid updates + * of the clock event device * * The hrtimer structure must be initialized by hrtimer_setup() */ @@ -45,6 +47,7 @@ struct hrtimer { u8 is_rel; u8 is_soft; u8 is_hard; + u8 is_lazy; }; #endif /* _LINUX_HRTIMER_TYPES_H */ diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index 67917ce696d4..e54f8b59f6b4 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1152,7 +1152,7 @@ static void __remove_hrtimer(struct hrtimer *timer, * an superfluous call to hrtimer_force_reprogram() on the * remote cpu later on if the same timer gets enqueued again. */ - if (reprogram && timer == cpu_base->next_timer) + if (reprogram && timer == cpu_base->next_timer && !timer->is_lazy) hrtimer_force_reprogram(cpu_base, 1); } @@ -1321,6 +1321,20 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, return 0; } + /* + * Special case for the HRTICK timer. It is frequently rearmed and most + * of the time moves the expiry into the future. That's expensive in + * virtual machines and it's better to take the pointless already armed + * interrupt than reprogramming the hardware on every context switch. + * + * If the new expiry is before the armed time, then reprogramming is + * required. + */ + if (timer->is_lazy) { + if (new_base->cpu_base->expires_next <= hrtimer_get_expires(timer)) + return 0; + } + /* * Timer was forced to stay on the current CPU to avoid * reprogramming on removal and enqueue. Force reprogram the @@ -1675,6 +1689,7 @@ static void __hrtimer_setup(struct hrtimer *timer, base += hrtimer_clockid_to_base(clock_id); timer->is_soft = softtimer; timer->is_hard = !!(mode & HRTIMER_MODE_HARD); + timer->is_lazy = !!(mode & HRTIMER_MODE_LAZY_REARM); timer->base = &cpu_base->clock_base[base]; timerqueue_init(&timer->node);