perf counters: implement PERF_COUNT_TASK_CLOCK

Impact: add new perf-counter type

The 'task clock' counter counts the amount of time a task is executing,
in nanoseconds. It stops ticking when a task is scheduled out either due
to it blocking, sleeping or it being preempted.

This counter type is a Linux kernel based abstraction, it is available
even if the hardware does not support native hardware performance counters.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/perf_counter.h

@@ -50,8 +50,11 @@ enum hw_event_types {
 	 */
 	PERF_COUNT_CPU_CLOCK		= -1,
 	PERF_COUNT_TASK_CLOCK		= -2,
-	PERF_COUNT_PAGE_FAULTS		= -3,
-	PERF_COUNT_CONTEXT_SWITCHES	= -4,
+	/*
+	 * Future software events:
+	 */
+	/* PERF_COUNT_PAGE_FAULTS	= -3,
+	   PERF_COUNT_CONTEXT_SWITCHES	= -4, */
 };
 
 /*

kernel/perf_counter.c

@@ -855,6 +855,25 @@ static const struct hw_perf_counter_ops perf_ops_cpu_clock = {
 	.hw_perf_counter_read		= cpu_clock_perf_counter_read,
 };
 
+static void task_clock_perf_counter_enable(struct perf_counter *counter)
+{
+}
+
+static void task_clock_perf_counter_disable(struct perf_counter *counter)
+{
+}
+
+static void task_clock_perf_counter_read(struct perf_counter *counter)
+{
+	atomic64_counter_set(counter, current->se.sum_exec_runtime);
+}
+
+static const struct hw_perf_counter_ops perf_ops_task_clock = {
+	.hw_perf_counter_enable		= task_clock_perf_counter_enable,
+	.hw_perf_counter_disable	= task_clock_perf_counter_disable,
+	.hw_perf_counter_read		= task_clock_perf_counter_read,
+};
+
 static const struct hw_perf_counter_ops *
 sw_perf_counter_init(struct perf_counter *counter)
 {
@@ -864,6 +883,9 @@ sw_perf_counter_init(struct perf_counter *counter)
 	case PERF_COUNT_CPU_CLOCK:
 		hw_ops = &perf_ops_cpu_clock;
 		break;
+	case PERF_COUNT_TASK_CLOCK:
+		hw_ops = &perf_ops_task_clock;
+		break;
 	default:
 		break;
 	}