eventlog: Dump cost centre stack on each sample

With this change it is possible to reconstruct the timing portion of a
`.prof` file after the fact. By logging the stacks at each time point
a more precise executation trace of the program can be observed rather
than all identical cost centres being identified in the report.

There are two new events:

1. `EVENT_PROF_BEGIN` - emitted at the start of profiling to communicate
the tick interval
2. `EVENT_PROF_SAMPLE_COST_CENTRE` - emitted on each tick to communicate the
current call stack.

Fixes #17322

1 files changed, 19 insertions, 1 deletions

diff --git a/rts/Profiling.c b/rts/Profiling.c
index b91129ed98..a4247c7809 100644
--- a/rts/Profiling.c
+++ b/rts/Profiling.c
@@ -25,7 +25,7 @@
 #include <fs_rts.h>
 #include <string.h>
 
-#if defined(DEBUG)
+#if defined(DEBUG) || defined(PROFILING)
 #include "Trace.h"
 #endif
 
@@ -132,6 +132,19 @@ static  void              initProfilingLogFile ( void );
    Initialise the profiling environment
    -------------------------------------------------------------------------- */
 
+static void
+dumpCostCentresToEventLog(void)
+{
+#if defined(PROFILING)
+    CostCentre *cc, *next;
+    for (cc = CC_LIST; cc != NULL; cc = next) {
+        next = cc->link;
+        traceHeapProfCostCentre(cc->ccID, cc->label, cc->module,
+                                cc->srcloc, cc->is_caf);
+    }
+#endif
+}
+
 void initProfiling (void)
 {
     // initialise our arena
@@ -187,8 +200,12 @@ void initProfiling (void)
     if (RtsFlags.CcFlags.doCostCentres) {
         initTimeProfiling();
     }
+
+    dumpCostCentresToEventLog();
 }
 
+
+
 //
 // Should be called after loading any new Haskell code.
 //
@@ -278,6 +295,7 @@ initProfilingLogFile(void)
 void
 initTimeProfiling(void)
 {
+    traceProfBegin();
     /* Start ticking */
     startProfTimer();
 };