[vm] Intern callstacks when writing Perfetto profile

This significantly reduces the space occupied by callstacks
e.g. 5 second recording of fibonacci computation goes from
1.5Mb to 600Kb.

Also fixes flakiness of pkg/vm_service/test/get_perfetto_cpu_samples_rpc_test.

Fixes #54401

TEST=ci

Change-Id: I6202ce7e87ceb64f4330b7052e72e519a848e571
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/417521
Reviewed-by: Derek Xu <[email protected]>

Author: mraleph

pkg/vm_service/test/get_perfetto_cpu_samples_rpc_test.dart

@@ -63,6 +63,19 @@ Iterable<PerfSample> extractPerfSamplesFromTracePackets(
 final tests = <IsolateTest>[
   hasStoppedAtExit,
   (VmService service, IsolateRef isolateRef) async {
+    // This test is calling |getPerfettoCpuSamples| twice: with and without
+    // filter and expects to get consistent results. However profiler will
+    // continue running and recording samples while this is happening which
+    // means the buffer can overflow and old samples will be lost.
+    //
+    // The best way to avoid this would be to pause the profiler, but
+    // service API does not provide a way to do it: setting profiler flag to
+    // false will stop profiler entirely and discard accumulated samples.
+    //
+    // Instead we resort to bumping profile_period to 1h to stabilize this
+    // test.
+    await service.setFlag('profile_period', '60000000');
+
     final result = await service.getPerfettoCpuSamples(isolateRef.id!);
     expect(result.type, 'PerfettoCpuSamples');
     expect(result.samplePeriod, isPositive);
@@ -77,18 +90,52 @@ final tests = <IsolateTest>[
     int frameCount = 0;
     int callstackCount = 0;
     int perfSampleCount = 0;
+    final seenFrames = <int>{};
+    final seenCallstacks = <int>{};
     for (final packet in packets) {
+      if (packet.sequenceFlags &
+              TracePacket_SequenceFlags.SEQ_INCREMENTAL_STATE_CLEARED.value !=
+          0) {
+        seenCallstacks.clear();
+      }
+
       if (packet.hasInternedData()) {
         frameCount += packet.internedData.frames.length;
         callstackCount += packet.internedData.callstacks.length;
+
+        for (var frame in packet.internedData.frames) {
+          expect(frame.iid.toInt(), isNot(0));
+          seenFrames.add(frame.iid.toInt());
+        }
+        for (var callstack in packet.internedData.callstacks) {
+          for (var frame in callstack.frameIds) {
+            expect(frame.toInt(), isIn(seenFrames));
+          }
+
+          expect(callstack.iid.toInt(), isNot(0));
+          seenCallstacks.add(callstack.iid.toInt());
+        }
       }
       if (packet.hasPerfSample()) {
         perfSampleCount += 1;
+
+        // Check that packet correctly indicates dependency on incremental
+        // state and that incremental state contains interned callstack
+        // for this sample.
+        expect(
+          packet.sequenceFlags &
+                  TracePacket_SequenceFlags.SEQ_NEEDS_INCREMENTAL_STATE.value !=
+              0,
+          isTrue,
+        );
+        expect(packet.perfSample.callstackIid.toInt(), isIn(seenCallstacks));
       }
     }
     expect(frameCount, isPositive);
     expect(callstackCount, isPositive);
-    expect(perfSampleCount, callstackCount);
+    // Note: we will have more perfSampleCount than we have callstacks because
+    // callstacks are interned.
+    expect(perfSampleCount, greaterThanOrEqualTo(callstackCount));
 
     // Calculate the time window of events.
     final timeOriginNanos = computeTimeOriginNanos(packets);

runtime/vm/profiler_service.cc

@@ -1665,13 +1665,14 @@ void Profile::ProcessSampleFrameJSON(JSONArray* stack,
 }
 
 #if defined(SUPPORT_PERFETTO) && !defined(PRODUCT)
-void Profile::ProcessSampleFramePerfetto(
-    perfetto::protos::pbzero::Callstack* callstack,
-    ProfileCodeInlinedFunctionsCache* cache,
-    ProcessedSample* sample,
-    intptr_t frame_index) {
+namespace {
+void ProcessSampleFramePerfetto(Profile* profile,
+                                GrowableArray<uint64_t>& callstack,
+                                ProfileCodeInlinedFunctionsCache* cache,
+                                ProcessedSample* sample,
+                                intptr_t frame_index) {
   const uword pc = sample->At(frame_index);
-  ProfileCode* profile_code = GetCodeFromPC(pc, sample->timestamp());
+  ProfileCode* profile_code = profile->GetCodeFromPC(pc, sample->timestamp());
   ASSERT(profile_code != nullptr);
   ProfileFunction* function = profile_code->function();
   ASSERT(function != nullptr);
@@ -1691,51 +1692,28 @@ void Profile::ProcessSampleFramePerfetto(
     code ^= profile_code->code().ptr();
     cache->Get(pc, code, sample, frame_index, &inlined_functions,
                &inlined_token_positions, &token_position);
-    if (FLAG_trace_profiler_verbose && (inlined_functions != NULL)) {
-      for (intptr_t i = 0; i < inlined_functions->length(); i++) {
-        const String& name =
-            String::Handle((*inlined_functions)[i]->QualifiedScrubbedName());
-        THR_Print("InlinedFunction[%" Pd "] = {%s, %s}\n", i, name.ToCString(),
-                  (*inlined_token_positions)[i].ToCString());
-      }
-    }
   }
 
   if (code.IsNull() || (inlined_functions == nullptr) ||
       (inlined_functions->length() <= 1)) {
     // This is the ID of a |Frame| that was added to the interned data table in
     // |ProfilerService::PrintProfilePerfetto|. See the comments in that method
     // for more details.
-    callstack->add_frame_ids(function->table_index() + 1);
+    callstack.Add(function->table_index() + 1);
     return;
   }
 
-  if (!code.is_optimized()) {
-    OS::PrintErr("Code that should be optimized is not. Please file a bug\n");
-    OS::PrintErr("Code object: %s\n", code.ToCString());
-    OS::PrintErr("Inlined functions length: %" Pd "\n",
-                 inlined_functions->length());
-    for (intptr_t i = 0; i < inlined_functions->length(); i++) {
-      OS::PrintErr("IF[%" Pd "] = %s\n", i,
-                   (*inlined_functions)[i]->ToFullyQualifiedCString());
-    }
-  }
-
-  ASSERT(code.is_optimized());
-
   for (intptr_t i = 0; i < inlined_functions->length(); ++i) {
     const Function* inlined_function = (*inlined_functions)[i];
     ASSERT(inlined_function != NULL);
     ASSERT(!inlined_function->IsNull());
     ProfileFunction* profile_function =
-        functions_->LookupOrAdd(*inlined_function);
+        profile->FindFunction(*inlined_function);
     ASSERT(profile_function != NULL);
-    // This is the ID of a |Frame| that was added to the interned data table in
-    // |ProfilerService::PrintProfilePerfetto|. See the comments in that method
-    // for more details.
-    callstack->add_frame_ids(profile_function->table_index() + 1);
+    callstack.Add(profile_function->table_index() + 1);
   }
 }
+}  // namespace
 #endif  // defined(SUPPORT_PERFETTO) && !defined(PRODUCT)
 
 void Profile::ProcessInlinedFunctionFrameJSON(
@@ -1824,13 +1802,32 @@ void Profile::PrintSamplesPerfetto(
   ASSERT(packet_ptr != nullptr);
   auto& packet = *packet_ptr;
 
+  perfetto_utils::BytesInterner<uint64_t, Zone> callstack_interner(zone_);
+  GrowableArray<uint64_t> callstack(128);
+
   // Note that |cache| is zone-allocated, so it does not need to be deallocated
   // manually.
   auto* cache = new ProfileCodeInlinedFunctionsCache();
   for (intptr_t sample_index = 0; sample_index < samples_->length();
        ++sample_index) {
     ProcessedSample* sample = samples_->At(sample_index);
 
+    // Walk the sampled PCs and intern the stack.
+    callstack.Clear();
+    for (intptr_t frame_index = sample->length() - 1; frame_index >= 0;
+         --frame_index) {
+      ASSERT(sample->At(frame_index) != 0);
+      ProcessSampleFramePerfetto(this, callstack, cache, sample, frame_index);
+    }
+
+    // Empty sample (everything is invisible).
+    if (callstack.is_empty()) {
+      continue;
+    }
+
+    const auto callstack_iid =
+        callstack_interner.Intern(&callstack[0], callstack.length());
+
     perfetto_utils::SetTrustedPacketSequenceId(packet.get());
     // We set this flag to indicate that this packet reads from the interned
     // data table.
@@ -1840,27 +1837,25 @@ void Profile::PrintSamplesPerfetto(
     perfetto_utils::SetTimestampAndMonotonicClockId(packet.get(),
                                                     sample->timestamp());
 
-    const intptr_t callstack_iid = sample_index + 1;
-    // Add a |Callstack| to the interned data table that represents the stack
-    // trace stored in |sample|.
-    perfetto::protos::pbzero::Callstack* callstack =
-        packet->set_interned_data()->add_callstacks();
-    callstack->set_iid(callstack_iid);
-    // Walk the sampled PCs.
-    for (intptr_t frame_index = sample->length() - 1; frame_index >= 0;
-         --frame_index) {
-      ASSERT(sample->At(frame_index) != 0);
-      ProcessSampleFramePerfetto(callstack, cache, sample, frame_index);
-    }
-
     // Populate |packet| with a |PerfSample| that is linked to the |Callstack|
     // that we populated above.
-    perfetto::protos::pbzero::PerfSample& perf_sample =
-        *packet->set_perf_sample();
+    auto& perf_sample = *packet->set_perf_sample();
     perf_sample.set_pid(OS::ProcessId());
     perf_sample.set_tid(OSThread::ThreadIdToIntPtr(sample->tid()));
     perf_sample.set_callstack_iid(callstack_iid);
 
+    if (callstack_interner.HasNewlyInternedEntries()) {
+      auto& interned_data = *packet->set_interned_data();
+      callstack_interner.FlushNewlyInternedTo(
+          [&interned_data](const auto& interned) {
+            auto& callstack = *interned_data.add_callstacks();
+            callstack.set_iid(interned.iid);
+            for (intptr_t i = 0; i < interned.length; i++) {
+              callstack.add_frame_ids(interned.data[i]);
+            }
+          });
+    }
+
     perfetto_utils::AppendPacketToJSONBase64String(jsonBase64String, &packet);
     packet.Reset();
   }

runtime/vm/profiler_service.h

@@ -406,13 +406,6 @@ class Profile : public ValueObject {
                               ProfileCodeInlinedFunctionsCache* cache,
                               ProcessedSample* sample,
                               intptr_t frame_index);
-#if defined(SUPPORT_PERFETTO) && !defined(PRODUCT)
-  void ProcessSampleFramePerfetto(
-      perfetto::protos::pbzero::Callstack* callstack,
-      ProfileCodeInlinedFunctionsCache* cache,
-      ProcessedSample* sample,
-      intptr_t frame_index);
-#endif  // defined(SUPPORT_PERFETTO) && !defined(PRODUCT)
   void ProcessInlinedFunctionFrameJSON(JSONArray* stack,
                                        const Function* inlined_function);
   void PrintFunctionFrameIndexJSON(JSONArray* stack, ProfileFunction* function);