Add new eventlog EVENT_WALL_CLOCK_TIME for time matching

Eventlog timestamps are elapsed times (in nanoseconds) relative to the
process start. To be able to merge eventlogs from multiple processes we
need to be able to align their timelines. If they share a clock domain
(or a user judges that their clocks are sufficiently closely
synchronised) then it is sufficient to know how the eventlog timestamps
match up with the clock.

The EVENT_WALL_CLOCK_TIME contains the clock time with (up to)
nanosecond precision. It is otherwise an ordinary event and so contains
the usual timestamp for the same moment in time. It therefore enables
us to match up all the eventlog timestamps with clock time.

1 files changed, 6 insertions, 0 deletions

diff --git a/rts/Trace.c b/rts/Trace.c
index 7aa0f7b444..9d29f2a8fa 100644
--- a/rts/Trace.c
+++ b/rts/Trace.c
@@ -328,6 +328,12 @@ void traceCapsetEvent_ (EventTypeNum tag,
     }
 }
 
+void traceWallClockTime_(void) {
+    if (eventlog_enabled) {
+        postWallClockTime(CAPSET_CLOCKDOMAIN_DEFAULT);
+    }
+}
+
 void traceOSProcessInfo_(void) {
     if (eventlog_enabled) {
         postCapsetEvent(EVENT_OSPROCESS_PID,