Commit 555e0c1e authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

perf: Migrate perf to use new tick dependency mask model 



Instead of providing asynchronous checks for the nohz subsystem to verify
perf event tick dependency, migrate perf to the new mask.

Perf needs the tick for two situations:

1) Freq events. We could set the tick dependency when those are
installed on a CPU context. But setting a global dependency on top of
the global freq events accounting is much easier. If people want that
to be optimized, we can still refine that on the per-CPU tick dependency
level. This patch dooesn't change the current behaviour anyway.

2) Throttled events: this is a per-cpu dependency.

Reviewed-by: default avatarChris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent e6e6cc22

include/linux/perf_event.h

+0 −6
Original line number Diff line number Diff line
@@ -1108,12 +1108,6 @@ static inline void perf_event_task_tick(void) { } 
static inline int perf_event_release_kernel(struct perf_event *event)	{ return 0; }

#endif



#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_NO_HZ_FULL)

extern bool perf_event_can_stop_tick(void);

#else

static inline bool perf_event_can_stop_tick(void)			{ return true; }

#endif



#if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)

extern void perf_restore_debug_store(void);

#else

include/linux/tick.h

+0 −2
Original line number Diff line number Diff line
@@ -233,7 +233,6 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal, 
		tick_nohz_dep_clear_signal(signal, bit);

}



extern void tick_nohz_full_kick(void);

extern void tick_nohz_full_kick_cpu(int cpu);

extern void tick_nohz_full_kick_all(void);

extern void __tick_nohz_task_switch(void);
@@ -260,7 +259,6 @@ static inline void tick_dep_clear_signal(struct signal_struct *signal, 
					 enum tick_dep_bits bit) { }



static inline void tick_nohz_full_kick_cpu(int cpu) { }

static inline void tick_nohz_full_kick(void) { }

static inline void tick_nohz_full_kick_all(void) { }

static inline void __tick_nohz_task_switch(void) { }

#endif

kernel/events/core.c

+48 −17
Original line number Diff line number Diff line
@@ -3060,17 +3060,6 @@ done: 
	return rotate;

}



#ifdef CONFIG_NO_HZ_FULL

bool perf_event_can_stop_tick(void)

{

	if (atomic_read(&nr_freq_events) ||

	    __this_cpu_read(perf_throttled_count))

		return false;

	else

		return true;

}

#endif



void perf_event_task_tick(void)

{

	struct list_head *head = this_cpu_ptr(&active_ctx_list);
@@ -3081,6 +3070,7 @@ void perf_event_task_tick(void) 


	__this_cpu_inc(perf_throttled_seq);

	throttled = __this_cpu_xchg(perf_throttled_count, 0);

	tick_dep_clear_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);



	list_for_each_entry_safe(ctx, tmp, head, active_ctx_list)

		perf_adjust_freq_unthr_context(ctx, throttled);
@@ -3511,6 +3501,28 @@ static void unaccount_event_cpu(struct perf_event *event, int cpu) 
		atomic_dec(&per_cpu(perf_cgroup_events, cpu));

}



#ifdef CONFIG_NO_HZ_FULL

static DEFINE_SPINLOCK(nr_freq_lock);

#endif



static void unaccount_freq_event_nohz(void)

{

#ifdef CONFIG_NO_HZ_FULL

	spin_lock(&nr_freq_lock);

	if (atomic_dec_and_test(&nr_freq_events))

		tick_nohz_dep_clear(TICK_DEP_BIT_PERF_EVENTS);

	spin_unlock(&nr_freq_lock);

#endif

}



static void unaccount_freq_event(void)

{

	if (tick_nohz_full_enabled())

		unaccount_freq_event_nohz();

	else

		atomic_dec(&nr_freq_events);

}



static void unaccount_event(struct perf_event *event)

{

	bool dec = false;
@@ -3527,7 +3539,7 @@ static void unaccount_event(struct perf_event *event) 
	if (event->attr.task)

		atomic_dec(&nr_task_events);

	if (event->attr.freq)

		atomic_dec(&nr_freq_events);

		unaccount_freq_event();

	if (event->attr.context_switch) {

		dec = true;

		atomic_dec(&nr_switch_events);
@@ -6349,9 +6361,9 @@ static int __perf_event_overflow(struct perf_event *event, 
		if (unlikely(throttle

			     && hwc->interrupts >= max_samples_per_tick)) {

			__this_cpu_inc(perf_throttled_count);

			tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);

			hwc->interrupts = MAX_INTERRUPTS;

			perf_log_throttle(event, 0);

			tick_nohz_full_kick();

			ret = 1;

		}

	}
@@ -7741,6 +7753,27 @@ static void account_event_cpu(struct perf_event *event, int cpu) 
		atomic_inc(&per_cpu(perf_cgroup_events, cpu));

}



/* Freq events need the tick to stay alive (see perf_event_task_tick). */

static void account_freq_event_nohz(void)

{

#ifdef CONFIG_NO_HZ_FULL

	/* Lock so we don't race with concurrent unaccount */

	spin_lock(&nr_freq_lock);

	if (atomic_inc_return(&nr_freq_events) == 1)

		tick_nohz_dep_set(TICK_DEP_BIT_PERF_EVENTS);

	spin_unlock(&nr_freq_lock);

#endif

}



static void account_freq_event(void)

{

	if (tick_nohz_full_enabled())

		account_freq_event_nohz();

	else

		atomic_inc(&nr_freq_events);

}





static void account_event(struct perf_event *event)

{

	bool inc = false;
@@ -7756,10 +7789,8 @@ static void account_event(struct perf_event *event) 
		atomic_inc(&nr_comm_events);

	if (event->attr.task)

		atomic_inc(&nr_task_events);

	if (event->attr.freq) {

		if (atomic_inc_return(&nr_freq_events) == 1)

			tick_nohz_full_kick_all();

	}

	if (event->attr.freq)

		account_freq_event();

	if (event->attr.context_switch) {

		atomic_inc(&nr_switch_events);

		inc = true;

kernel/time/tick-sched.c

+1 −7
Original line number Diff line number Diff line
@@ -22,7 +22,6 @@ 
#include <linux/module.h>

#include <linux/irq_work.h>

#include <linux/posix-timers.h>

#include <linux/perf_event.h>

#include <linux/context_tracking.h>



#include <asm/irq_regs.h>
@@ -215,11 +214,6 @@ static bool can_stop_full_tick(struct tick_sched *ts) 
		return false;

	}



	if (!perf_event_can_stop_tick()) {

		trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);

		return false;

	}



#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

	/*

	 * sched_clock_tick() needs us?
@@ -257,7 +251,7 @@ static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = { 
 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),

 * is NMI safe.

 */

void tick_nohz_full_kick(void)

static void tick_nohz_full_kick(void)

{

	if (!tick_nohz_full_cpu(smp_processor_id()))

		return;

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