[llvm-exegesis] Make createCounter a virtual method on Target to allow targets to create target-specific counters

[oontvoo]

Summary

Context: Split off from https://reviews.llvm.org/D77422

[oontvoo]

fix accidentally mixed-up branches

P.S: actually still not fixed. i've sorted out the branches locally and re-run arc diff but that didn't seem to fix it. Any idea which else to try?

[courbet]

Can you also include making the Counter virtual, and the use of this new function in FunctionExecutorImpl::runAndMeasure ? This would remove more unrelated changes from the other patch.

[oontvoo]

Move non-LBR related changes from benchmarkrunner and PerfHelper over too.

[oontvoo]

Sync/rebase

[courbet]

LGTM modulo one comment.

llvm/tools/llvm-exegesis/lib/PerfHelper.h

85

I don't think this needs to be virtual, does it ? readOrError is the real thing.

[oontvoo]

Make read() non-virtual

[oontvoo]

Committed (cc8fafa2be8d5315cc55aec54b2a6d7e60f470c4)

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

 //===-- BenchmarkRunner.cpp -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include <array>
+#include <memory>
 #include <string>
 
 #include "Assembler.h"
 #include "BenchmarkRunner.h"
 #include "Error.h"
 #include "MCInstrDescView.h"
 #include "PerfHelper.h"
+#include "Target.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CrashRecoveryContext.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Program.h"
 
 namespace llvm {
 namespace exegesis {
 
 BenchmarkRunner::BenchmarkRunner(const LLVMState &State,
                                  InstructionBenchmark::ModeE Mode)
     : State(State), Mode(Mode), Scratch(std::make_unique<ScratchSpace>()) {}
 
 BenchmarkRunner::~BenchmarkRunner() = default;
 
 namespace {
 class FunctionExecutorImpl : public BenchmarkRunner::FunctionExecutor {
 public:
   FunctionExecutorImpl(const LLVMState &State,
                        object::OwningBinary<object::ObjectFile> Obj,
                        BenchmarkRunner::ScratchSpace *Scratch)
-      : Function(State.createTargetMachine(), std::move(Obj)),
+      : State(State), Function(State.createTargetMachine(), std::move(Obj)),
         Scratch(Scratch) {}
 
 private:
   Expected<int64_t> runAndMeasure(const char *Counters) const override {
     // We sum counts when there are several counters for a single ProcRes
     // (e.g. P23 on SandyBridge).
     int64_t CounterValue = 0;
     SmallVector<StringRef, 2> CounterNames;
     StringRef(Counters).split(CounterNames, '+');
     char *const ScratchPtr = Scratch->ptr();
     for (auto &CounterName : CounterNames) {
       CounterName = CounterName.trim();
-      pfm::PerfEvent PerfEvent(CounterName);
-      if (!PerfEvent.valid())
-        return make_error<Failure>(
-            Twine("invalid perf event '").concat(CounterName).concat("'"));
-      pfm::Counter Counter(std::move(PerfEvent));
+      auto CounterOrError =
+          State.getExegesisTarget().createCounter(CounterName.data(), State);
+
+      if (!CounterOrError)
+        return CounterOrError.takeError();
+
+      pfm::Counter *Counter = CounterOrError.get().get();
       Scratch->clear();
       {
         CrashRecoveryContext CRC;
         CrashRecoveryContext::Enable();
-        const bool Crashed = !CRC.RunSafely([this, &Counter, ScratchPtr]() {
-          Counter.start();
+        const bool Crashed = !CRC.RunSafely([this, Counter, ScratchPtr]() {
+          Counter->start();
           this->Function(ScratchPtr);
-          Counter.stop();
+          Counter->stop();
         });
         CrashRecoveryContext::Disable();
         // FIXME: Better diagnosis.
         if (Crashed)
           return make_error<SnippetCrash>("snippet crashed while running");
       }
-      CounterValue += Counter.read();
+      CounterValue += Counter->read();
     }
     return CounterValue;
   }
 
+  const LLVMState &State;
   const ExecutableFunction Function;
   BenchmarkRunner::ScratchSpace *const Scratch;
 };
 } // namespace
 
 Expected<InstructionBenchmark> BenchmarkRunner::runConfiguration(
     const BenchmarkCode &BC, unsigned NumRepetitions,
     ArrayRef<std::unique_ptr<const SnippetRepetitor>> Repetitors,

llvm/tools/llvm-exegesis/lib/PerfHelper.h

 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
 #define LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/Error.h"
+#include <cstdint>
 #include <functional>
 #include <memory>
 
 struct perf_event_attr;
 
 namespace llvm {
 namespace exegesis {
 namespace pfm {
 
 // Returns true on error.
 bool pfmInitialize();
 void pfmTerminate();
 
 // Retrieves the encoding for the event described by pfm_event_string.
 // NOTE: pfm_initialize() must be called before creating PerfEvent objects.
 class PerfEvent {
 public:
   // http://perfmon2.sourceforge.net/manv4/libpfm.html
   // Events are expressed as strings. e.g. "INSTRUCTION_RETIRED"
-  explicit PerfEvent(StringRef pfm_event_string);
+  explicit PerfEvent(StringRef PfmEventString);
 
   PerfEvent(const PerfEvent &) = delete;
   PerfEvent(PerfEvent &&other);
   ~PerfEvent();
 
   // The pfm_event_string passed at construction time.
   StringRef name() const;
 

 private:
   const std::string EventString;
   std::string FullQualifiedEventString;
   perf_event_attr *Attr;
 };
 
 // Uses a valid PerfEvent to configure the Kernel so we can measure the
 // underlying event.
-struct Counter {
+class Counter {
+public:
   // event: the PerfEvent to measure.
   explicit Counter(PerfEvent &&event);
 
   Counter(const Counter &) = delete;
   Counter(Counter &&other) = default;
 
-  ~Counter();
+  virtual ~Counter();
+
+  /// Starts the measurement of the event.
+  virtual void start();
+
+  /// Stops the measurement of the event.
+  void stop();
+
+  /// Returns the current value of the counter or -1 if it cannot be read.
+  int64_t read() const;
 
-  void start();         // Starts the measurement of the event.
-  void stop();          // Stops the measurement of the event.
-  int64_t read() const; // Return the current value of the counter.
+  /// Returns the current value of the counter or error if it cannot be read.
+  virtual llvm::Expected<int64_t> readOrError() const;
 
 private:
   PerfEvent Event;
 #ifdef HAVE_LIBPFM
   int FileDescriptor = -1;
 #endif
 };
 
 } // namespace pfm
 } // namespace exegesis
 } // namespace llvm
 
 #endif // LLVM_TOOLS_LLVM_EXEGESIS_PERFHELPER_H

llvm/tools/llvm-exegesis/lib/PerfHelper.cpp

 //===-- PerfHelper.cpp ------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "PerfHelper.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
 #ifdef HAVE_LIBPFM
 #include "perfmon/perf_event.h"
 #include "perfmon/pfmlib.h"
 #include "perfmon/pfmlib_perf_event.h"
 #endif
+
 #include <cassert>
+#include <cstddef>
+#include <errno.h>  // for erno
+#include <string.h> // for strerror()
 
 namespace llvm {
 namespace exegesis {
 namespace pfm {
 
 #ifdef HAVE_LIBPFM
 static bool isPfmError(int Code) { return Code != PFM_SUCCESS; }
 #endif
Counter::Counter(PerfEvent &&E) : Event(std::move(E)){
   assert(Event.valid());
   const pid_t Pid = 0;    // measure current process/thread.
   const int Cpu = -1;     // measure any processor.
   const int GroupFd = -1; // no grouping of counters.
   const uint32_t Flags = 0;
   perf_event_attr AttrCopy = *Event.attribute();
   FileDescriptor = perf_event_open(&AttrCopy, Pid, Cpu, GroupFd, Flags);
   if (FileDescriptor == -1) {
-    errs() << "Unable to open event, make sure your kernel allows user "
+    errs() << "Unable to open event. ERRNO: " << strerror(errno)
+           << ". Make sure your kernel allows user "
               "space perf monitoring.\nYou may want to try:\n$ sudo sh "
               "-c 'echo -1 > /proc/sys/kernel/perf_event_paranoid'\n";
   }
   assert(FileDescriptor != -1 && "Unable to open event");
 }
 
 Counter::~Counter() { close(FileDescriptor); }
 
 void Counter::start() { ioctl(FileDescriptor, PERF_EVENT_IOC_RESET, 0); }
 
 void Counter::stop() { ioctl(FileDescriptor, PERF_EVENT_IOC_DISABLE, 0); }
 
 int64_t Counter::read() const {
+  auto ValueOrError = readOrError();
+  if (ValueOrError)
+    return ValueOrError.get();
+
+  errs() << ValueOrError.takeError() << "\n";
+  return -1;
+}
+
+llvm::Expected<int64_t> Counter::readOrError() const {
   int64_t Count = 0;
   ssize_t ReadSize = ::read(FileDescriptor, &Count, sizeof(Count));
-  if (ReadSize != sizeof(Count)) {
-    Count = -1;
-    errs() << "Failed to read event counter\n";
-  }
+  if (ReadSize != sizeof(Count))
+    return llvm::make_error<llvm::StringError>("Failed to read event counter",
+                                               llvm::errc::io_error);
+
   return Count;
 }
 
 #else
 
 Counter::Counter(PerfEvent &&Event) : Event(std::move(Event)) {}
 
 Counter::~Counter() = default;
 
 void Counter::start() {}
 
 void Counter::stop() {}
 
 int64_t Counter::read() const { return 42; }
 
+llvm::Expected<int64_t> Counter::readOrError() const {
+  return llvm::make_error<llvm::StringError>("Not implemented",
+                                             llvm::errc::io_error);
+}
+
 #endif
 
 } // namespace pfm
 } // namespace exegesis
 } // namespace llvm

llvm/tools/llvm-exegesis/lib/Target.h

 
 #ifndef LLVM_TOOLS_LLVM_EXEGESIS_TARGET_H
 #define LLVM_TOOLS_LLVM_EXEGESIS_TARGET_H
 
 #include "BenchmarkResult.h"
 #include "BenchmarkRunner.h"
 #include "Error.h"
 #include "LlvmState.h"
+#include "PerfHelper.h"
 #include "SnippetGenerator.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
 #include "llvm/IR/CallingConv.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCRegisterInfo.h"
+#include "llvm/Support/Error.h"
 
 namespace llvm {
 namespace exegesis {
 
 struct PfmCountersInfo {
   // An optional name of a performance counter that can be used to measure
   // cycles.
   const char *CycleCounter;
struct CpuAndPfmCounters {
   bool operator<(StringRef S) const { return StringRef(CpuName) < S; }
 };
 
 class ExegesisTarget {
 public:
   explicit ExegesisTarget(ArrayRef<CpuAndPfmCounters> CpuPfmCounters)
       : CpuPfmCounters(CpuPfmCounters) {}
 
+  // Targets can use this to create target-specific perf counters.
+  virtual Expected<std::unique_ptr<pfm::Counter>>
+  createCounter(const char *CounterName, const LLVMState &State) const;
+
   // Targets can use this to add target-specific passes in assembleToStream();
   virtual void addTargetSpecificPasses(PassManagerBase &PM) const {}
 
   // Generates code to move a constant into a the given register.
   // Precondition: Value must fit into Reg.
   virtual std::vector<MCInst> setRegTo(const MCSubtargetInfo &STI, unsigned Reg,
                                        const APInt &Value) const = 0;
 

llvm/tools/llvm-exegesis/lib/Target.cpp

 //===-- Target.cpp ----------------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 #include "Target.h"
 
 #include "LatencyBenchmarkRunner.h"
 #include "ParallelSnippetGenerator.h"
 #include "SerialSnippetGenerator.h"
 #include "UopsBenchmarkRunner.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/Error.h"
 
 namespace llvm {
 namespace exegesis {
 
 ExegesisTarget::~ExegesisTarget() {} // anchor.
 
 static ExegesisTarget *FirstTarget = nullptr;
 
 const ExegesisTarget *ExegesisTarget::lookup(Triple TT) {
   for (const ExegesisTarget *T = FirstTarget; T != nullptr; T = T->Next) {
     if (T->matchesArch(TT.getArch()))
       return T;
   }
   return nullptr;
 }
 
+Expected<std::unique_ptr<pfm::Counter>>
+ExegesisTarget::createCounter(const char *CounterName,
+                              const LLVMState &) const {
+  pfm::PerfEvent Event(CounterName);
+  if (!Event.valid())
+    return llvm::make_error<Failure>(
+        llvm::Twine("Unable to create counter with name '")
+            .concat(CounterName)
+            .concat("'"));
+
+  return std::make_unique<pfm::Counter>(std::move(Event));
+}
+
 void ExegesisTarget::registerTarget(ExegesisTarget *Target) {
   if (FirstTarget == nullptr) {
     FirstTarget = Target;
     return;
   }
   if (Target->Next != nullptr)
     return; // Already registered.
   Target->Next = FirstTarget;