Merging r354764:

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r354764 | lebedevri | 2019-02-25 08:39:07 +0100 (Mon, 25 Feb 2019) | 123 lines

[XRay][tools] Revert "Use Support/JSON.h in llvm-xray convert"

Summary:
This reverts D50129 / rL338834: [XRay][tools] Use Support/JSON.h in llvm-xray convert

Abstractions are great.
Readable code is great.
JSON support library is a *good* idea.

However unfortunately, there is an internal detail that one needs
to be aware of in `llvm::json::Object` - it uses `llvm::DenseMap`.
So for **every** `llvm::json::Object`, even if you only store a single `int`
entry there, you pay the whole price of `llvm::DenseMap`.

Unfortunately, it matters for `llvm-xray`.

I was trying to analyse the `llvm-exegesis` analysis mode performance,
and for that i wanted to view the LLVM X-Ray log visualization in Chrome
trace viewer. And the `llvm-xray convert` is sluggish, and sometimes
even ended up being killed by OOM.

`xray-log.llvm-exegesis.lwZ0sT` was acquired from `llvm-exegesis`
(compiled with ` -fxray-instruction-threshold=128`)
analysis mode over `-benchmarks-file` with 10099 points (one full
latency measurement set), with normal runtime of 0.387s.

Timings:
Old: (copied from D58580)
```
$ perf stat -r 5 ./bin/llvm-xray convert -sort -symbolize -instr_map=./bin/llvm-exegesis -output-format=trace_event -output=/tmp/trace.yml xray-log.llvm-exegesis.lwZ0sT

 Performance counter stats for './bin/llvm-xray convert -sort -symbolize -instr_map=./bin/llvm-exegesis -output-format=trace_event -output=/tmp/trace.yml xray-log.llvm-exegesis.lwZ0sT' (5 runs):

          21346.24 msec task-clock                #    1.000 CPUs utilized            ( +-  0.28% )
               314      context-switches          #   14.701 M/sec                    ( +- 59.13% )
                 1      cpu-migrations            #    0.037 M/sec                    ( +-100.00% )
           2181354      page-faults               # 102191.251 M/sec                  ( +-  0.02% )
       85477442102      cycles                    # 4004415.019 GHz                   ( +-  0.28% )  (83.33%)
       14526427066      stalled-cycles-frontend   #   16.99% frontend cycles idle     ( +-  0.70% )  (83.33%)
       32371533721      stalled-cycles-backend    #   37.87% backend cycles idle      ( +-  0.27% )  (33.34%)
       67896890228      instructions              #    0.79  insn per cycle
                                                  #    0.48  stalled cycles per insn  ( +-  0.03% )  (50.00%)
       14592654840      branches                  # 683631198.653 M/sec               ( +-  0.02% )  (66.67%)
         212207534      branch-misses             #    1.45% of all branches          ( +-  0.94% )  (83.34%)

           21.3502 +- 0.0585 seconds time elapsed  ( +-  0.27% )
```
New:
```
$ perf stat -r 9 ./bin/llvm-xray convert -sort -symbolize -instr_map=./bin/llvm-exegesis -output-format=trace_event -output=/tmp/trace.yml xray-log.llvm-exegesis.lwZ0sT

 Performance counter stats for './bin/llvm-xray convert -sort -symbolize -instr_map=./bin/llvm-exegesis -output-format=trace_event -output=/tmp/trace.yml xray-log.llvm-exegesis.lwZ0sT' (9 runs):

           7178.38 msec task-clock                #    1.000 CPUs utilized            ( +-  0.26% )
               182      context-switches          #   25.402 M/sec                    ( +- 28.84% )
                 0      cpu-migrations            #    0.046 M/sec                    ( +- 70.71% )
             33701      page-faults               # 4694.994 M/sec                    ( +-  0.88% )
       28761053971      cycles                    # 4006833.933 GHz                   ( +-  0.26% )  (83.32%)
        2028297997      stalled-cycles-frontend   #    7.05% frontend cycles idle     ( +-  1.61% )  (83.32%)
       10773154901      stalled-cycles-backend    #   37.46% backend cycles idle      ( +-  0.38% )  (33.36%)
       36199132874      instructions              #    1.26  insn per cycle
                                                  #    0.30  stalled cycles per insn  ( +-  0.03% )  (50.02%)
        6434504227      branches                  # 896420204.421 M/sec               ( +-  0.03% )  (66.68%)
          73355176      branch-misses             #    1.14% of all branches          ( +-  1.46% )  (83.33%)

            7.1807 +- 0.0190 seconds time elapsed  ( +-  0.26% )
```

So using `llvm::json` nearly triples run-time on that test case.
(+3x is times, not percent.)

Memory:
Old:
```
total runtime: 39.88s.
bytes allocated in total (ignoring deallocations): 79.07GB (1.98GB/s)
calls to allocation functions: 33267816 (834135/s)
temporary memory allocations: 5832298 (146235/s)
peak heap memory consumption: 9.21GB
peak RSS (including heaptrack overhead): 147.98GB
total memory leaked: 1.09MB
```
New:
```
total runtime: 17.42s.
bytes allocated in total (ignoring deallocations): 5.12GB (293.86MB/s)
calls to allocation functions: 21382982 (1227284/s)
temporary memory allocations: 232858 (13364/s)
peak heap memory consumption: 350.69MB
peak RSS (including heaptrack overhead): 2.55GB
total memory leaked: 79.95KB
```
Diff:
```
total runtime: -22.46s.
bytes allocated in total (ignoring deallocations): -73.95GB (3.29GB/s)
calls to allocation functions: -11884834 (529155/s)
temporary memory allocations: -5599440 (249307/s)
peak heap memory consumption: -8.86GB
peak RSS (including heaptrack overhead): 0B
total memory leaked: -1.01MB
```
So using `llvm::json` increases *peak* memory consumption on *this* testcase ~+27x.
And total allocation count +15x. Both of these numbers are times, *not* percent.

And note that memory usage is clearly unbound with `llvm::json`, it directly depends
on the length of the log, so peak memory consumption is always increasing.
This isn't so with the dumb code, there is no accumulating memory consumption,
peak memory consumption is fixed. Naturally, that means it will handle *much*
larger logs without OOM'ing.

Readability is good, but the price is simply unacceptable here.
Too bad none of this analysis was done as part of the development/review D50129 itself.

Reviewers: dberris, kpw, sammccall

Reviewed By: dberris

Subscribers: riccibruno, hans, courbet, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58584
------------------------------------------------------------------------


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_80@354856 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 61 insertions, 48 deletions

diff --git a/tools/llvm-xray/xray-converter.cpp b/tools/llvm-xray/xray-converter.cpp
index 3f153b99bc93..a682dbe53e3b 100644
--- a/tools/llvm-xray/xray-converter.cpp
+++ b/tools/llvm-xray/xray-converter.cpp
@@ -18,7 +18,6 @@
 #include "llvm/Support/EndianStream.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FormatVariadic.h"
-#include "llvm/Support/JSON.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/YAMLTraits.h"
 #include "llvm/Support/raw_ostream.h"
@@ -242,6 +241,31 @@ StackTrieNode *findOrCreateStackNode(
   return CurrentStack;
 }
 
+void writeTraceViewerRecord(uint16_t Version, raw_ostream &OS, int32_t FuncId,
+                            uint32_t TId, uint32_t PId, bool Symbolize,
+                            const FuncIdConversionHelper &FuncIdHelper,
+                            double EventTimestampUs,
+                            const StackTrieNode &StackCursor,
+                            StringRef FunctionPhenotype) {
+  OS << "    ";
+  if (Version >= 3) {
+    OS << llvm::formatv(
+        R"({ "name" : "{0}", "ph" : "{1}", "tid" : "{2}", "pid" : "{3}", )"
+        R"("ts" : "{4:f4}", "sf" : "{5}" })",
+        (Symbolize ? FuncIdHelper.SymbolOrNumber(FuncId)
+                   : llvm::to_string(FuncId)),
+        FunctionPhenotype, TId, PId, EventTimestampUs,
+        StackCursor.ExtraData.id);
+  } else {
+    OS << llvm::formatv(
+        R"({ "name" : "{0}", "ph" : "{1}", "tid" : "{2}", "pid" : "1", )"
+        R"("ts" : "{3:f3}", "sf" : "{4}" })",
+        (Symbolize ? FuncIdHelper.SymbolOrNumber(FuncId)
+                   : llvm::to_string(FuncId)),
+        FunctionPhenotype, TId, EventTimestampUs, StackCursor.ExtraData.id);
+  }
+}
+
 } // namespace
 
 void TraceConverter::exportAsChromeTraceEventFormat(const Trace &Records,
@@ -252,14 +276,18 @@ void TraceConverter::exportAsChromeTraceEventFormat(const Trace &Records,
 
   unsigned id_counter = 0;
 
+  OS << "{\n  \"traceEvents\": [";
   DenseMap<uint32_t, StackTrieNode *> StackCursorByThreadId{};
   DenseMap<uint32_t, SmallVector<StackTrieNode *, 4>> StackRootsByThreadId{};
   DenseMap<unsigned, StackTrieNode *> StacksByStackId{};
   std::forward_list<StackTrieNode> NodeStore{};
-
-  // Create a JSON Array which will hold all trace events.
-  json::Array TraceEvents;
+  int loop_count = 0;
   for (const auto &R : Records) {
+    if (loop_count++ == 0)
+      OS << "\n";
+    else
+      OS << ",\n";
+
     // Chrome trace event format always wants data in micros.
     // CyclesPerMicro = CycleHertz / 10^6
     // TSC / CyclesPerMicro == TSC * 10^6 / CycleHertz == MicroTimestamp
@@ -284,15 +312,8 @@ void TraceConverter::exportAsChromeTraceEventFormat(const Trace &Records,
       // type of B for begin or E for end, thread id, process id,
       // timestamp in microseconds, and a stack frame id. The ids are logged
       // in an id dictionary after the events.
-      TraceEvents.push_back(json::Object({
-          {"name", Symbolize ? FuncIdHelper.SymbolOrNumber(R.FuncId)
-                             : llvm::to_string(R.FuncId)},
-          {"ph", "B"},
-          {"tid", llvm::to_string(R.TId)},
-          {"pid", llvm::to_string(Version >= 3 ? R.PId : 1)},
-          {"ts", llvm::formatv("{0:f4}", EventTimestampUs)},
-          {"sf", llvm::to_string(StackCursor->ExtraData.id)},
-      }));
+      writeTraceViewerRecord(Version, OS, R.FuncId, R.TId, R.PId, Symbolize,
+                             FuncIdHelper, EventTimestampUs, *StackCursor, "B");
       break;
     case RecordTypes::EXIT:
     case RecordTypes::TAIL_EXIT:
@@ -303,51 +324,43 @@ void TraceConverter::exportAsChromeTraceEventFormat(const Trace &Records,
       // (And/Or in loop termination below)
       StackTrieNode *PreviousCursor = nullptr;
       do {
-        TraceEvents.push_back(json::Object({
-            {"name", Symbolize
-                         ? FuncIdHelper.SymbolOrNumber(StackCursor->FuncId)
-                         : llvm::to_string(StackCursor->FuncId)},
-            {"ph", "E"},
-            {"tid", llvm::to_string(R.TId)},
-            {"pid", llvm::to_string(Version >= 3 ? R.PId : 1)},
-            {"ts", llvm::formatv("{0:f4}", EventTimestampUs)},
-            {"sf", llvm::to_string(StackCursor->ExtraData.id)},
-        }));
+        if (PreviousCursor != nullptr) {
+          OS << ",\n";
+        }
+        writeTraceViewerRecord(Version, OS, StackCursor->FuncId, R.TId, R.PId,
+                               Symbolize, FuncIdHelper, EventTimestampUs,
+                               *StackCursor, "E");
         PreviousCursor = StackCursor;
         StackCursor = StackCursor->Parent;
       } while (PreviousCursor->FuncId != R.FuncId && StackCursor != nullptr);
       break;
     }
   }
+  OS << "\n  ],\n"; // Close the Trace Events array.
+  OS << "  "
+     << "\"displayTimeUnit\": \"ns\",\n";
 
   // The stackFrames dictionary substantially reduces size of the output file by
   // avoiding repeating the entire call stack of function names for each entry.
-  json::Object StackFrames;
-  for (const auto &Stack : StacksByStackId) {
-    const auto &StackId = Stack.first;
-    const auto &StackFunctionNode = Stack.second;
-    json::Object::iterator It;
-    std::tie(It, std::ignore) = StackFrames.insert({
-        llvm::to_string(StackId),
-        json::Object{
-            {"name",
-             Symbolize ? FuncIdHelper.SymbolOrNumber(StackFunctionNode->FuncId)
-                       : llvm::to_string(StackFunctionNode->FuncId)}},
-    });
-
-    if (StackFunctionNode->Parent != nullptr)
-      It->second.getAsObject()->insert(
-          {"parent", llvm::to_string(StackFunctionNode->Parent->ExtraData.id)});
+  OS << R"(  "stackFrames": {)";
+  int stack_frame_count = 0;
+  for (auto map_iter : StacksByStackId) {
+    if (stack_frame_count++ == 0)
+      OS << "\n";
+    else
+      OS << ",\n";
+    OS << "    ";
+    OS << llvm::formatv(
+        R"("{0}" : { "name" : "{1}")", map_iter.first,
+        (Symbolize ? FuncIdHelper.SymbolOrNumber(map_iter.second->FuncId)
+                   : llvm::to_string(map_iter.second->FuncId)));
+    if (map_iter.second->Parent != nullptr)
+      OS << llvm::formatv(R"(, "parent": "{0}")",
+                          map_iter.second->Parent->ExtraData.id);
+    OS << " }";
   }
-
-  json::Object TraceJSON{
-      {"displayTimeUnit", "ns"},
-      {"traceEvents", std::move(TraceEvents)},
-      {"stackFrames", std::move(StackFrames)},
-  };
-
-  // Pretty-print the JSON using two spaces for indentations.
-  OS << formatv("{0:2}", json::Value(std::move(TraceJSON)));
+  OS << "\n  }\n"; // Close the stack frames map.
+  OS << "}\n";     // Close the JSON entry.
 }
 
 namespace llvm {