[compiler-rt] r345954 - [XRay] Update delta computations in runtime

[Dean Michael Berris via llvm-commits]

Author: dberris
Date: Fri Nov  2 01:07:38 2018
New Revision: 345954

URL: http://llvm.org/viewvc/llvm-project?rev=345954&view=rev
Log:
[XRay] Update delta computations in runtime

Summary:
Fix some issues discovered from mostly manual inspection of outputs from
the `llvm-xray fdr-dump` tool.

It turns out we haven't been writing the deltas properly, and have been
writing down zeros for deltas of some records. This change fixes this
oversight born by the recent refactoring.

Reviewers: mboerger

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D54022

Modified:
    compiler-rt/trunk/lib/xray/tests/unit/fdr_controller_test.cc
    compiler-rt/trunk/lib/xray/xray_fdr_controller.h

Modified: compiler-rt/trunk/lib/xray/tests/unit/fdr_controller_test.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/tests/unit/fdr_controller_test.cc?rev=345954&r1=345953&r2=345954&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/tests/unit/fdr_controller_test.cc (original)
+++ compiler-rt/trunk/lib/xray/tests/unit/fdr_controller_test.cc Fri Nov  2 01:07:38 2018
@@ -137,6 +137,30 @@ TEST_F(FunctionSequenceTest, PreservedCa
                 TSCIs(Gt(1000uL))))));
 }
 
+TEST_F(FunctionSequenceTest, PreservedCallsSupportLargeDeltas) {
+  C = llvm::make_unique<FDRController<>>(BQ.get(), B, *W, clock_gettime, 1000);
+  uint64_t TSC = 1;
+  uint16_t CPU = 0;
+  const auto LargeDelta = uint64_t{std::numeric_limits<int32_t>::max()};
+  ASSERT_TRUE(C->functionEnter(1, TSC++, CPU));
+  ASSERT_TRUE(C->functionExit(1, TSC += LargeDelta, CPU));
+  ASSERT_TRUE(C->flush());
+  ASSERT_EQ(BQ->finalize(), BufferQueue::ErrorCode::Ok);
+
+  // Serialize the buffer then test to see if we find the right TSC with a large
+  // delta.
+  std::string Serialized = serialize(*BQ, 3);
+  llvm::DataExtractor DE(Serialized, true, 8);
+  auto TraceOrErr = llvm::xray::loadTrace(DE);
+  EXPECT_THAT_EXPECTED(
+      TraceOrErr,
+      HasValue(ElementsAre(
+          AllOf(FuncId(1), RecordType(llvm::xray::RecordTypes::ENTER),
+                TSCIs(Eq(1uL))),
+          AllOf(FuncId(1), RecordType(llvm::xray::RecordTypes::EXIT),
+                TSCIs(Gt(LargeDelta))))));
+}
+
 TEST_F(FunctionSequenceTest, RewindingMultipleCalls) {
   C = llvm::make_unique<FDRController<>>(BQ.get(), B, *W, clock_gettime, 1000);
 

Modified: compiler-rt/trunk/lib/xray/xray_fdr_controller.h
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_fdr_controller.h?rev=345954&r1=345953&r2=345954&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_fdr_controller.h (original)
+++ compiler-rt/trunk/lib/xray/xray_fdr_controller.h Fri Nov  2 01:07:38 2018
@@ -13,6 +13,7 @@
 #ifndef COMPILER_RT_LIB_XRAY_XRAY_FDR_CONTROLLER_H_
 #define COMPILER_RT_LIB_XRAY_XRAY_FDR_CONTROLLER_H_
 
+#include <limits>
 #include <time.h>
 
 #include "xray/xray_interface.h"
@@ -158,8 +159,14 @@ template <size_t Version = 3> class FDRC
       return PreambleResult::WroteMetadata;
     }
 
-    if (UNLIKELY(LatestCPU == LatestCPU && LatestTSC > TSC)) {
-      // The TSC has wrapped around, from the last TSC we've seen.
+    DCHECK_EQ(LatestCPU, CPU);
+
+    if (UNLIKELY(LatestTSC > TSC ||
+                 TSC - LatestTSC >
+                     uint64_t{std::numeric_limits<int32_t>::max()})) {
+      // Either the TSC has wrapped around from the last TSC we've seen or the
+      // delta is too large to fit in a 32-bit signed integer, so we write a
+      // wrap-around record.
       LatestTSC = TSC;
 
       if (B.Generation != BQ->generation())
@@ -248,10 +255,11 @@ public:
     UndoableFunctionEnters = (PreambleStatus == PreambleResult::WroteMetadata)
                                  ? 1
                                  : UndoableFunctionEnters + 1;
+    auto Delta = TSC - LatestTSC;
     LastFunctionEntryTSC = TSC;
     LatestTSC = TSC;
     return W.writeFunction(FDRLogWriter::FunctionRecordKind::Enter,
-                           mask(FuncId), TSC - LatestTSC);
+                           mask(FuncId), Delta);
   }
 
   bool functionTailExit(int32_t FuncId, uint64_t TSC,
@@ -273,9 +281,10 @@ public:
 
     UndoableTailExits = UndoableFunctionEnters ? UndoableTailExits + 1 : 0;
     UndoableFunctionEnters = 0;
+    auto Delta = TSC - LatestTSC;
     LatestTSC = TSC;
     return W.writeFunction(FDRLogWriter::FunctionRecordKind::TailExit,
-                           mask(FuncId), TSC - LatestTSC);
+                           mask(FuncId), Delta);
   }
 
   bool functionEnterArg(int32_t FuncId, uint64_t TSC, uint16_t CPU,
@@ -285,13 +294,14 @@ public:
         functionPreamble(TSC, CPU) == PreambleResult::InvalidBuffer)
       return returnBuffer();
 
+    auto Delta = TSC - LatestTSC;
     LatestTSC = TSC;
     LastFunctionEntryTSC = 0;
     UndoableFunctionEnters = 0;
     UndoableTailExits = 0;
 
     W.writeFunction(FDRLogWriter::FunctionRecordKind::EnterArg, mask(FuncId),
-                    TSC - LatestTSC);
+                    Delta);
     return W.writeMetadata<MetadataRecord::RecordKinds::CallArgument>(Arg);
   }