[counters] Add --slow-histograms flag

The V8.Execute histogram is not free and can cause more overhead
than expected. This CL is guarding slower histograms behind a new
--slow-histograms flag.

For now --slow-histograms is enabled by default. Once all
chrome-side changes and benchmark changes have landed it will be
disabled by default.

--dump-counters will automatically enable --slow-histograms.

The goal is to not report slow histograms on UMA by default on stable:
- 100% reporting on canary/dev/beta
- 1% reporting on stable or specific finch experiments

Chrome-side feature: https://crrev.com/c/3065464

Bug: v8:11946
Change-Id: I23c782288e10ceb76323d72eceea9170739fd543
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3067318
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76041}

src/flags/flag-definitions.h

@@ -1784,6 +1784,9 @@ DEFINE_BOOL_READONLY(minor_mc, false,
 
 DEFINE_BOOL(help, false, "Print usage message, including flags, on console")
 DEFINE_BOOL(dump_counters, false, "Dump counters on exit")
+DEFINE_BOOL(slow_histograms, true, "Enable slow histograms with more overhead.")
+DEFINE_IMPLICATION(dump_counters, slow_histograms)
+
 DEFINE_BOOL(dump_counters_nvp, false,
             "Dump counters as name-value pairs on exit")
 DEFINE_BOOL(use_external_strings, false, "Use external strings for source code")

src/logging/counters-definitions.h

@@ -124,12 +124,14 @@ namespace internal {
      MICROSECOND)                                                              \
   /* Total compilation time incl. caching/parsing */                           \
   HT(compile_script, V8.CompileScriptMicroSeconds, 1000000, MICROSECOND)       \
-  /* Total JavaScript execution time (including callbacks and runtime calls */ \
-  HT(execute, V8.Execute, 1000000, MICROSECOND)                                \
   /* Time for lazily compiling Wasm functions. */                              \
   HT(wasm_lazy_compile_time, V8.WasmLazyCompileTimeMicroSeconds, 100000000,    \
      MICROSECOND)
 
+#define HISTOGRAM_TIMER_LIST_SLOW(HT)                                          \
+  /* Total JavaScript execution time (including callbacks and runtime calls */ \
+  HT(execute, V8.Execute, 1000000, MICROSECOND)
+
 #define TIMED_HISTOGRAM_LIST(HT)                                               \
   /* Timer histograms, thread safe: HT(name, caption, max, unit) */            \
   /* Garbage collection timers. */                                             \

src/logging/counters.cc

@@ -156,7 +156,7 @@ Counters::Counters(Isolate* isolate)
   } kHistogramTimers[] = {
 #define HT(name, caption, max, res) \
   {&Counters::name##_, #caption, max, HistogramTimerResolution::res},
-      HISTOGRAM_TIMER_LIST(HT)
+      HISTOGRAM_TIMER_LIST(HT) HISTOGRAM_TIMER_LIST_SLOW(HT)
 #undef HT
   };
   for (const auto& timer : kHistogramTimers) {
@@ -300,6 +300,10 @@ void Counters::ResetCreateHistogramFunction(CreateHistogramCallback f) {
   HISTOGRAM_TIMER_LIST(HT)
 #undef HT
 
+#define HT(name, caption, max, res) name##_.Reset(FLAG_slow_histograms);
+  HISTOGRAM_TIMER_LIST_SLOW(HT)
+#undef HT
+
 #define HT(name, caption, max, res) name##_.Reset();
   TIMED_HISTOGRAM_LIST(HT)
 #undef HT

src/logging/counters.h

@@ -242,7 +242,9 @@ class Histogram {
   Counters* counters() const { return counters_; }
 
   // Reset the cached internal pointer.
-  void Reset() { histogram_ = CreateHistogram(); }
+  void Reset(bool create_new = true) {
+    histogram_ = create_new ? CreateHistogram() : nullptr;
+  }
 
  private:
   friend class Counters;
@@ -674,6 +676,7 @@ class Counters : public std::enable_shared_from_this<Counters> {
 #define HT(name, caption, max, res) \
   HistogramTimer* name() { return &name##_; }
   HISTOGRAM_TIMER_LIST(HT)
+  HISTOGRAM_TIMER_LIST_SLOW(HT)
 #undef HT
 
 #define HT(name, caption, max, res) \
@@ -712,6 +715,7 @@ class Counters : public std::enable_shared_from_this<Counters> {
   enum Id {
 #define RATE_ID(name, caption, max, res) k_##name,
     HISTOGRAM_TIMER_LIST(RATE_ID)
+    HISTOGRAM_TIMER_LIST_SLOW(RATE_ID)
     TIMED_HISTOGRAM_LIST(RATE_ID)
 #undef RATE_ID
 #define AGGREGATABLE_ID(name, caption) k_##name,
@@ -784,6 +788,7 @@ class Counters : public std::enable_shared_from_this<Counters> {
 
 #define HT(name, caption, max, res) HistogramTimer name##_;
   HISTOGRAM_TIMER_LIST(HT)
+  HISTOGRAM_TIMER_LIST_SLOW(HT)
 #undef HT
 
 #define HT(name, caption, max, res) TimedHistogram name##_;