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>

2 files changed, 27 insertions, 2 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 68f6e3ad531f..30c0ec8c1ee3 100644
--- a/include/linux/perf_counter.h
+++ b/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, */
 };
 
 /*
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 0e93fea17120..a0fe8474ee29 100644
--- a/kernel/perf_counter.c
+++ b/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;
         }