[tip:perf/core] perf: Per cpu-context rotation timer

tip-bot for Peter Zijlstra
2010-09-09T19:52:04Z

Commit-ID: b5ab4cd563e7ab49b27957704112a8ecade54e1f
Gitweb: http://git.kernel.org/tip/b5ab4cd563e7ab49b27957704112a8ecade54e1f
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Mon, 6 Sep 2010 16:32:21 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 9 Sep 2010 20:46:32 +0200

perf: Per cpu-context rotation timer

Give each cpu-context its own timer so that it is a self contained
entity, this eases the way for per-pmu-per-cpu contexts as well as
provides the basic infrastructure to allow different rotation
times per pmu.

Things to look at:
- folding the tick and these TICK_NSEC timers
- separate task context rotation

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus <paulus@samba.org>
Cc: stephane eranian <eranian@googlemail.com>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Yanmin <yanmin_zhang@linux.intel.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/perf_event.h | 5 +--
kernel/perf_event.c | 80 ++++++++++++++++++++++++++++++++++---------
kernel/sched.c | 2 -
3 files changed, 65 insertions(+), 22 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4ab4f0c..fa04537 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -861,6 +861,8 @@ struct perf_cpu_context {
struct perf_event_context *task_ctx;
int active_oncpu;
int exclusive;
+ u64 timer_interval;
+ struct hrtimer timer;
};

struct perf_output_handle {
@@ -881,7 +883,6 @@ extern void perf_pmu_unregister(struct pmu *pmu);

extern void perf_event_task_sched_in(struct task_struct *task);
extern void perf_event_task_sched_out(struct task_struct *task, struct task_struct *next);
-extern void perf_event_task_tick(struct task_struct *task);
extern int perf_event_init_task(struct task_struct *child);
extern void perf_event_exit_task(struct task_struct *child);
extern void perf_event_free_task(struct task_struct *task);
@@ -1067,8 +1068,6 @@ perf_event_task_sched_in(struct task_struct *task) { }
static inline void
perf_event_task_sched_out(struct task_struct *task,
struct task_struct *next) { }
-static inline void
-perf_event_task_tick(struct task_struct *task) { }
static inline int perf_event_init_task(struct task_struct *child) { return 0; }
static inline void perf_event_exit_task(struct task_struct *child) { }
static inline void perf_event_free_task(struct task_struct *task) { }
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 2c47ed6..d75e4c8 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -78,6 +78,25 @@ void perf_pmu_enable(struct pmu *pmu)
pmu->pmu_enable(pmu);
}

+static void perf_pmu_rotate_start(void)
+{
+ struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+
+ if (hrtimer_active(&cpuctx->timer))
+ return;
+
+ __hrtimer_start_range_ns(&cpuctx->timer,
+ ns_to_ktime(cpuctx->timer_interval), 0,
+ HRTIMER_MODE_REL_PINNED, 0);
+}
+
+static void perf_pmu_rotate_stop(void)
+{
+ struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+
+ hrtimer_cancel(&cpuctx->timer);
+}
+
static void get_ctx(struct perf_event_context *ctx)
{
WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
@@ -281,6 +300,8 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
}

list_add_rcu(&event->event_entry, &ctx->event_list);
+ if (!ctx->nr_events)
+ perf_pmu_rotate_start();
ctx->nr_events++;
if (event->attr.inherit_stat)
ctx->nr_stat++;
@@ -1383,6 +1404,12 @@ void perf_event_task_sched_in(struct task_struct *task)
ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE);

cpuctx->task_ctx = ctx;
+
+ /*
+ * Since these rotations are per-cpu, we need to ensure the
+ * cpu-context we got scheduled on is actually rotating.
+ */
+ perf_pmu_rotate_start();
}

#define MAX_INTERRUPTS (~0ULL)
@@ -1487,7 +1514,7 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
}
}

-static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
+static void perf_ctx_adjust_freq(struct perf_event_context *ctx, u64 period)
{
struct perf_event *event;
struct hw_perf_event *hwc;
@@ -1524,7 +1551,7 @@ static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
hwc->freq_count_stamp = now;

if (delta > 0)
- perf_adjust_period(event, TICK_NSEC, delta);
+ perf_adjust_period(event, period, delta);
}
raw_spin_unlock(&ctx->lock);
}
@@ -1542,30 +1569,39 @@ static void rotate_ctx(struct perf_event_context *ctx)
raw_spin_unlock(&ctx->lock);
}

-void perf_event_task_tick(struct task_struct *curr)
+/*
+ * Cannot race with ->pmu_rotate_start() because this is ran from hardirq
+ * context, and ->pmu_rotate_start() is called with irqs disabled (both are
+ * cpu affine, so there are no SMP races).
+ */
+static enum hrtimer_restart perf_event_context_tick(struct hrtimer *timer)
{
+ enum hrtimer_restart restart = HRTIMER_NORESTART;
struct perf_cpu_context *cpuctx;
struct perf_event_context *ctx;
int rotate = 0;

- if (!atomic_read(&nr_events))
- return;
+ cpuctx = container_of(timer, struct perf_cpu_context, timer);

- cpuctx = &__get_cpu_var(perf_cpu_context);
- if (cpuctx->ctx.nr_events &&
- cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
- rotate = 1;
+ if (cpuctx->ctx.nr_events) {
+ restart = HRTIMER_RESTART;
+ if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
+ rotate = 1;
+ }

- ctx = curr->perf_event_ctxp;
- if (ctx && ctx->nr_events && ctx->nr_events != ctx->nr_active)
- rotate = 1;
+ ctx = current->perf_event_ctxp;
+ if (ctx && ctx->nr_events) {
+ restart = HRTIMER_RESTART;
+ if (ctx->nr_events != ctx->nr_active)
+ rotate = 1;
+ }

- perf_ctx_adjust_freq(&cpuctx->ctx);
+ perf_ctx_adjust_freq(&cpuctx->ctx, cpuctx->timer_interval);
if (ctx)
- perf_ctx_adjust_freq(ctx);
+ perf_ctx_adjust_freq(ctx, cpuctx->timer_interval);

if (!rotate)
- return;
+ goto done;

cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
if (ctx)
@@ -1577,7 +1613,12 @@ void perf_event_task_tick(struct task_struct *curr)

cpu_ctx_sched_in(cpuctx, EVENT_FLEXIBLE);
if (ctx)
- task_ctx_sched_in(curr, EVENT_FLEXIBLE);
+ task_ctx_sched_in(current, EVENT_FLEXIBLE);
+
+done:
+ hrtimer_forward_now(timer, ns_to_ktime(cpuctx->timer_interval));
+
+ return restart;
}

static int event_enable_on_exec(struct perf_event *event,
@@ -4786,7 +4827,7 @@ static void perf_swevent_start_hrtimer(struct perf_event *event)
}
__hrtimer_start_range_ns(&hwc->hrtimer,
ns_to_ktime(period), 0,
- HRTIMER_MODE_REL, 0);
+ HRTIMER_MODE_REL_PINNED, 0);
}
}

@@ -5904,6 +5945,9 @@ static void __init perf_event_init_all_cpus(void)

cpuctx = &per_cpu(perf_cpu_context, cpu);
__perf_event_init_context(&cpuctx->ctx, NULL);
+ cpuctx->timer_interval = TICK_NSEC;
+ hrtimer_init(&cpuctx->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ cpuctx->timer.function = perf_event_context_tick;
}
}

@@ -5934,6 +5978,8 @@ static void __perf_event_exit_cpu(void *info)
struct perf_event_context *ctx = &cpuctx->ctx;
struct perf_event *event, *tmp;

+ perf_pmu_rotate_stop();
+
list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
__perf_event_remove_from_context(event);
list_for_each_entry_safe(event, tmp, &ctx->flexible_groups, group_entry)
diff --git a/kernel/sched.c b/kernel/sched.c
index 09b574e..66a02ba 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3578,8 +3578,6 @@ void scheduler_tick(void)
curr->sched_class->task_tick(rq, curr, 0);
raw_spin_unlock(&rq->lock);

- perf_event_task_tick(curr);
-
#ifdef CONFIG_SMP
rq->idle_at_tick = idle_cpu(cpu);
trigger_load_balance(rq, cpu);