hrtimer integration: properly trace late-added timers

When tasks add timers that have already expired (e.g., when preempted
during schedule_hrtimeout), we should not use the expriration time as
the reference time point, but rather the time when the timer was added
(the delay then includes activation of ksoftirqd, etc.).

2 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 720063df0ac0..dcbbd65c8af1 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -109,7 +109,7 @@ struct hrtimer {
         void                            *start_site;
         char                            start_comm[16];
 #endif
-#ifdef CONFIG_REPORT_TIMER_LATENCY
+#if defined(CONFIG_REPORT_TIMER_LATENCY) || defined(CONFIG_SCHED_OVERHEAD_TRACE)
         ktime_t when_added;
 #endif
 };
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index b4824e1dbc6d..c367854ce1d6 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1491,12 +1491,17 @@ static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
         t->task = NULL;
         if (task)
         {
+#ifdef CONFIG_SCHED_OVERHEAD_TRACE
                 if (is_realtime(task))
                 {
                         ktime_t expires = hrtimer_get_expires(timer);
-                        lt_t intended_release = ktime_to_ns(expires);
+                        /* Fix up timers that were added past their due date;
+                         * that's not really release latency. */
+                        lt_t intended_release = max(expires.tv64,
+                                                    timer->when_added.tv64);
                         TS_RELEASE_LATENCY(intended_release);
                 }
+#endif
                 TS_RELEASE_START;
                 wake_up_process(task);
                 TS_RELEASE_END;