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Date: Mon, 14 Dec 2015 19:38:28 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Chris Metcalf <cmetcalf@...hip.com>,
Thomas Gleixner <tglx@...utronix.de>,
Luiz Capitulino <lcapitulino@...hat.com>,
Christoph Lameter <cl@...ux.com>,
Ingo Molnar <mingo@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Rik van Riel <riel@...hat.com>
Subject: [PATCH 5/9] 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.
Cc: Christoph Lameter <cl@...ux.com>
Cc: Chris Metcalf <cmetcalf@...hip.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
include/linux/perf_event.h | 6 -----
include/linux/tick.h | 2 --
kernel/events/core.c | 65 ++++++++++++++++++++++++++++++++++------------
kernel/time/tick-sched.c | 8 +-----
4 files changed, 49 insertions(+), 32 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d841d33..56ff20f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1109,12 +1109,6 @@ 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
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 6d09dc1..eab61d0 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -178,7 +178,6 @@ extern void tick_nohz_set_dep_signal(struct signal_struct *signal,
extern void tick_nohz_clear_dep_signal(struct signal_struct *signal,
enum tick_dependency_bit 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);
@@ -205,7 +204,6 @@ static inline void tick_nohz_clear_dep_signal(enum tick_dependency_bit bit,
struct task_struct *signal) { }
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
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 36babfd..0802499 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3100,17 +3100,6 @@ 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);
@@ -3121,6 +3110,7 @@ void perf_event_task_tick(void)
__this_cpu_inc(perf_throttled_seq);
throttled = __this_cpu_xchg(perf_throttled_count, 0);
+ tick_nohz_clear_dep_cpu(TICK_PERF_EVENTS_BIT, smp_processor_id());
list_for_each_entry_safe(ctx, tmp, head, active_ctx_list)
perf_adjust_freq_unthr_context(ctx, throttled);
@@ -3573,6 +3563,28 @@ 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_clear_dep(TICK_PERF_EVENTS_BIT);
+ 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)
{
if (event->parent)
@@ -3587,7 +3599,7 @@ 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) {
static_key_slow_dec_deferred(&perf_sched_events);
atomic_dec(&nr_switch_events);
@@ -6402,9 +6414,9 @@ 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_nohz_set_dep_cpu(TICK_PERF_EVENTS_BIT, smp_processor_id());
hwc->interrupts = MAX_INTERRUPTS;
perf_log_throttle(event, 0);
- tick_nohz_full_kick();
ret = 1;
}
}
@@ -7804,6 +7816,27 @@ 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_set_dep(TICK_PERF_EVENTS_BIT);
+ 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)
{
if (event->parent)
@@ -7817,10 +7850,8 @@ 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);
static_key_slow_inc(&perf_sched_events.key);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b3bd5c4..00c20db 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -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>
@@ -213,11 +212,6 @@ static bool can_stop_full_tick(struct tick_sched *ts)
return false;
}
- if (!perf_event_can_stop_tick()) {
- trace_tick_stop(0, TICK_PERF_EVENTS_MASK);
- return false;
- }
-
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
/*
* sched_clock_tick() needs us?
@@ -255,7 +249,7 @@ 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;
--
2.6.4
--
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