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Subject[tip:perf/core] perf: Undo the per cpu-context timer stuff
Commit-ID:  e9d2b064149ff7ef4acbc65a1b9374ac8b218d3e
Gitweb: http://git.kernel.org/tip/e9d2b064149ff7ef4acbc65a1b9374ac8b218d3e
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 17 Sep 2010 11:28:50 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 17 Sep 2010 12:48:48 +0200

perf: Undo the per cpu-context timer stuff

Revert the timer per cpu-context timers because of unfortunate
nohz interaction. Fixing that would have been somewhat ugly, so
go back to driving things from the regular tick. Provide a
jiffies interval feature for people who want slower rotations.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20100917093009.519845633@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/linux/perf_event.h | 6 ++-
kernel/perf_event.c | 79 +++++++++++++++++++++++++++----------------
kernel/sched.c | 2 +
3 files changed, 55 insertions(+), 32 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 165287f..61b1e2d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -870,8 +870,8 @@ struct perf_cpu_context {
struct perf_event_context *task_ctx;
int active_oncpu;
int exclusive;
- u64 timer_interval;
- struct hrtimer timer;
+ struct list_head rotation_list;
+ int jiffies_interval;
};

struct perf_output_handle {
@@ -1065,6 +1065,7 @@ extern int perf_swevent_get_recursion_context(void);
extern void perf_swevent_put_recursion_context(int rctx);
extern void perf_event_enable(struct perf_event *event);
extern void perf_event_disable(struct perf_event *event);
+extern void perf_event_task_tick(void);
#else
static inline void
perf_event_task_sched_in(struct task_struct *task) { }
@@ -1099,6 +1100,7 @@ static inline int perf_swevent_get_recursion_context(void) { return -1; }
static inline void perf_swevent_put_recursion_context(int rctx) { }
static inline void perf_event_enable(struct perf_event *event) { }
static inline void perf_event_disable(struct perf_event *event) { }
+static inline void perf_event_task_tick(void) { }
#endif

#define perf_output_put(handle, x) \
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 27332e5..baae136 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -77,23 +77,22 @@ void perf_pmu_enable(struct pmu *pmu)
pmu->pmu_enable(pmu);
}

+static DEFINE_PER_CPU(struct list_head, rotation_list);
+
+/*
+ * perf_pmu_rotate_start() and perf_rotate_context() are fully serialized
+ * because they're strictly cpu affine and rotate_start is called with IRQs
+ * disabled, while rotate_context is called from IRQ context.
+ */
static void perf_pmu_rotate_start(struct pmu *pmu)
{
struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+ struct list_head *head = &__get_cpu_var(rotation_list);

- if (hrtimer_active(&cpuctx->timer))
- return;
+ WARN_ON(!irqs_disabled());

- __hrtimer_start_range_ns(&cpuctx->timer,
- ns_to_ktime(cpuctx->timer_interval), 0,
- HRTIMER_MODE_REL_PINNED, 0);
-}
-
-static void perf_pmu_rotate_stop(struct pmu *pmu)
-{
- struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
-
- hrtimer_cancel(&cpuctx->timer);
+ if (list_empty(&cpuctx->rotation_list))
+ list_add(&cpuctx->rotation_list, head);
}

static void get_ctx(struct perf_event_context *ctx)
@@ -1607,36 +1606,33 @@ static void rotate_ctx(struct perf_event_context *ctx)
}

/*
- * 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).
+ * perf_pmu_rotate_start() and perf_rotate_context() are fully serialized
+ * because they're strictly cpu affine and rotate_start is called with IRQs
+ * disabled, while rotate_context is called from IRQ context.
*/
-static enum hrtimer_restart perf_event_context_tick(struct hrtimer *timer)
+static void perf_rotate_context(struct perf_cpu_context *cpuctx)
{
- enum hrtimer_restart restart = HRTIMER_NORESTART;
- struct perf_cpu_context *cpuctx;
+ u64 interval = (u64)cpuctx->jiffies_interval * TICK_NSEC;
struct perf_event_context *ctx = NULL;
- int rotate = 0;
-
- cpuctx = container_of(timer, struct perf_cpu_context, timer);
+ int rotate = 0, remove = 1;

if (cpuctx->ctx.nr_events) {
- restart = HRTIMER_RESTART;
+ remove = 0;
if (cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
rotate = 1;
}

ctx = cpuctx->task_ctx;
if (ctx && ctx->nr_events) {
- restart = HRTIMER_RESTART;
+ remove = 0;
if (ctx->nr_events != ctx->nr_active)
rotate = 1;
}

perf_pmu_disable(cpuctx->ctx.pmu);
- perf_ctx_adjust_freq(&cpuctx->ctx, cpuctx->timer_interval);
+ perf_ctx_adjust_freq(&cpuctx->ctx, interval);
if (ctx)
- perf_ctx_adjust_freq(ctx, cpuctx->timer_interval);
+ perf_ctx_adjust_freq(ctx, interval);

if (!rotate)
goto done;
@@ -1654,10 +1650,24 @@ static enum hrtimer_restart perf_event_context_tick(struct hrtimer *timer)
task_ctx_sched_in(ctx, EVENT_FLEXIBLE);

done:
+ if (remove)
+ list_del_init(&cpuctx->rotation_list);
+
perf_pmu_enable(cpuctx->ctx.pmu);
- hrtimer_forward_now(timer, ns_to_ktime(cpuctx->timer_interval));
+}
+
+void perf_event_task_tick(void)
+{
+ struct list_head *head = &__get_cpu_var(rotation_list);
+ struct perf_cpu_context *cpuctx, *tmp;

- return restart;
+ WARN_ON(!irqs_disabled());
+
+ list_for_each_entry_safe(cpuctx, tmp, head, rotation_list) {
+ if (cpuctx->jiffies_interval == 1 ||
+ !(jiffies % cpuctx->jiffies_interval))
+ perf_rotate_context(cpuctx);
+ }
}

static int event_enable_on_exec(struct perf_event *event,
@@ -5186,9 +5196,8 @@ int perf_pmu_register(struct pmu *pmu)
__perf_event_init_context(&cpuctx->ctx);
cpuctx->ctx.type = cpu_context;
cpuctx->ctx.pmu = pmu;
- cpuctx->timer_interval = TICK_NSEC;
- hrtimer_init(&cpuctx->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
- cpuctx->timer.function = perf_event_context_tick;
+ cpuctx->jiffies_interval = 1;
+ INIT_LIST_HEAD(&cpuctx->rotation_list);
}

got_cpu_context:
@@ -6229,6 +6238,7 @@ static void __init perf_event_init_all_cpus(void)
for_each_possible_cpu(cpu) {
swhash = &per_cpu(swevent_htable, cpu);
mutex_init(&swhash->hlist_mutex);
+ INIT_LIST_HEAD(&per_cpu(rotation_list, cpu));
}
}

@@ -6248,6 +6258,15 @@ static void __cpuinit perf_event_init_cpu(int cpu)
}

#ifdef CONFIG_HOTPLUG_CPU
+static void perf_pmu_rotate_stop(struct pmu *pmu)
+{
+ struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+
+ WARN_ON(!irqs_disabled());
+
+ list_del_init(&cpuctx->rotation_list);
+}
+
static void __perf_event_exit_context(void *__info)
{
struct perf_event_context *ctx = __info;
diff --git a/kernel/sched.c b/kernel/sched.c
index 1c3ea7a..794819e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3584,6 +3584,8 @@ void scheduler_tick(void)
curr->sched_class->task_tick(rq, curr, 0);
raw_spin_unlock(&rq->lock);

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

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