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>

2 files changed, 51 insertions, 30 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 27332e5f51a7..baae1367e945 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 1c3ea7a55b7b..794819eab9ca 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);