[llvm] [llvm-exegesis] Enable dummy perf counters in subprocess mode (PR #74224)
Aiden Grossman via llvm-commits
llvm-commits at lists.llvm.org
Sat Dec 2 20:18:14 PST 2023
https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/74224
This patch enables the usage of dummy perf counters in the subprocess execution mode. This allows for users without libpfm installed/without access to performance counters to still use the subprocess execution mode to test the execution of snippets. This enables use cases like deriving memory annotations inside a virtual machine where performance counters will not be present.
>From d5081e46a12e5714c97463135ab2b20c89e69585 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <agrossman154 at yahoo.com>
Date: Sat, 2 Dec 2023 20:01:50 -0800
Subject: [PATCH] [llvm-exegesis] Enable dummy perf counters in subprocess mode
This patch enables the usage of dummy perf counters in the subprocess
execution mode. This allows for users without libpfm installed/without
access to performance counters to still use the subprocess execution
mode to test the execution of snippets. This enables use cases like
deriving memory annotations inside a virtual machine where performance
counters will not be present.
---
.../X86/dummy-perf-counters-subprocess.s | 7 --
.../latency/dummy-perf-counters-subprocess.s | 9 +++
llvm/tools/llvm-exegesis/lib/Assembler.cpp | 19 +++--
llvm/tools/llvm-exegesis/lib/Assembler.h | 6 +-
.../llvm-exegesis/lib/BenchmarkRunner.cpp | 72 +++++++++++++++----
llvm/tools/llvm-exegesis/lib/LlvmState.cpp | 8 ++-
llvm/tools/llvm-exegesis/lib/LlvmState.h | 6 +-
.../llvm-exegesis/lib/SnippetRepetitor.cpp | 9 ++-
llvm/tools/llvm-exegesis/llvm-exegesis.cpp | 5 --
.../llvm-exegesis/Common/AssemblerUtils.h | 2 +-
10 files changed, 100 insertions(+), 43 deletions(-)
delete mode 100644 llvm/test/tools/llvm-exegesis/X86/dummy-perf-counters-subprocess.s
create mode 100644 llvm/test/tools/llvm-exegesis/X86/latency/dummy-perf-counters-subprocess.s
diff --git a/llvm/test/tools/llvm-exegesis/X86/dummy-perf-counters-subprocess.s b/llvm/test/tools/llvm-exegesis/X86/dummy-perf-counters-subprocess.s
deleted file mode 100644
index d810d697ca273..0000000000000
--- a/llvm/test/tools/llvm-exegesis/X86/dummy-perf-counters-subprocess.s
+++ /dev/null
@@ -1,7 +0,0 @@
-# REQUIRES: exegesis-can-measure-latency, x86_64-linux
-
-# RUN: not llvm-exegesis -mtriple=x86_64-unknown-unknown -mode=latency -snippets-file=%s -execution-mode=subprocess -use-dummy-perf-counters 2>&1 | FileCheck %s
-
-# CHECK: llvm-exegesis error: Dummy perf counters are not supported in the subprocess execution mode.
-
-mov $0, %rax
diff --git a/llvm/test/tools/llvm-exegesis/X86/latency/dummy-perf-counters-subprocess.s b/llvm/test/tools/llvm-exegesis/X86/latency/dummy-perf-counters-subprocess.s
new file mode 100644
index 0000000000000..f5b40fbba28dd
--- /dev/null
+++ b/llvm/test/tools/llvm-exegesis/X86/latency/dummy-perf-counters-subprocess.s
@@ -0,0 +1,9 @@
+# REQUIRES: exegesis-can-execute-x86_64, x86_64-linux
+
+# RUN: llvm-exegesis -mtriple=x86_64-unknown-unknown -mcpu=x86-64 -mode=latency -snippets-file=%s -execution-mode=subprocess --use-dummy-perf-counters | FileCheck %s
+
+# LLVM-EXEGESIS-DEFREG RAX 0
+
+movq $5, %rax
+
+# CHECK: measurements: []
diff --git a/llvm/tools/llvm-exegesis/lib/Assembler.cpp b/llvm/tools/llvm-exegesis/lib/Assembler.cpp
index e17d239faa47e..cf5281556d536 100644
--- a/llvm/tools/llvm-exegesis/lib/Assembler.cpp
+++ b/llvm/tools/llvm-exegesis/lib/Assembler.cpp
@@ -48,7 +48,8 @@ static const Align kFunctionAlignment(4096);
static bool generateSnippetSetupCode(
const ExegesisTarget &ET, const MCSubtargetInfo *const MSI,
ArrayRef<RegisterValue> RegisterInitialValues, BasicBlockFiller &BBF,
- const BenchmarkKey &Key, bool GenerateMemoryInstructions) {
+ const BenchmarkKey &Key, bool GenerateMemoryInstructions,
+ bool UseDummyPerfCounters) {
bool IsSnippetSetupComplete = true;
if (GenerateMemoryInstructions) {
BBF.addInstructions(ET.generateMemoryInitialSetup());
@@ -80,7 +81,8 @@ static bool generateSnippetSetupCode(
}
if (GenerateMemoryInstructions) {
#ifdef HAVE_LIBPFM
- BBF.addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_RESET, true));
+ if (!UseDummyPerfCounters)
+ BBF.addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_RESET, true));
#endif // HAVE_LIBPFM
for (const RegisterValue &RV : RegisterInitialValues) {
// Load in the stack register now as we're done using it elsewhere
@@ -170,11 +172,14 @@ void BasicBlockFiller::addInstructions(ArrayRef<MCInst> Insts,
}
void BasicBlockFiller::addReturn(const ExegesisTarget &ET,
- bool SubprocessCleanup, const DebugLoc &DL) {
+ bool SubprocessCleanup,
+ bool UseDummyPerfCounters,
+ const DebugLoc &DL) {
// Insert cleanup code
if (SubprocessCleanup) {
#ifdef HAVE_LIBPFM
- addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_DISABLE, false));
+ if (!UseDummyPerfCounters)
+ addInstructions(ET.configurePerfCounter(PERF_EVENT_IOC_DISABLE, false));
#endif // HAVE_LIBPFM
#ifdef __linux__
addInstructions(ET.generateExitSyscall(0));
@@ -234,8 +239,8 @@ Error assembleToStream(const ExegesisTarget &ET,
ArrayRef<unsigned> LiveIns,
ArrayRef<RegisterValue> RegisterInitialValues,
const FillFunction &Fill, raw_pwrite_stream &AsmStream,
- const BenchmarkKey &Key,
- bool GenerateMemoryInstructions) {
+ const BenchmarkKey &Key, bool GenerateMemoryInstructions,
+ bool UseDummyPerfCounters) {
auto Context = std::make_unique<LLVMContext>();
std::unique_ptr<Module> Module =
createModule(Context, TM->createDataLayout());
@@ -284,7 +289,7 @@ Error assembleToStream(const ExegesisTarget &ET,
const bool IsSnippetSetupComplete = generateSnippetSetupCode(
ET, TM->getMCSubtargetInfo(), RegisterInitialValues, Entry, Key,
- GenerateMemoryInstructions);
+ GenerateMemoryInstructions, UseDummyPerfCounters);
// If the snippet setup is not complete, we disable liveliness tracking. This
// means that we won't know what values are in the registers.
diff --git a/llvm/tools/llvm-exegesis/lib/Assembler.h b/llvm/tools/llvm-exegesis/lib/Assembler.h
index abc5aa7be8cfe..166a1c2020bfb 100644
--- a/llvm/tools/llvm-exegesis/lib/Assembler.h
+++ b/llvm/tools/llvm-exegesis/lib/Assembler.h
@@ -51,7 +51,7 @@ class BasicBlockFiller {
void addInstructions(ArrayRef<MCInst> Insts, const DebugLoc &DL = DebugLoc());
void addReturn(const ExegesisTarget &ET, bool SubprocessCleanup,
- const DebugLoc &DL = DebugLoc());
+ bool UseDummyPerfCounters, const DebugLoc &DL = DebugLoc());
MachineFunction &MF;
MachineBasicBlock *const MBB;
@@ -93,8 +93,8 @@ Error assembleToStream(const ExegesisTarget &ET,
ArrayRef<unsigned> LiveIns,
ArrayRef<RegisterValue> RegisterInitialValues,
const FillFunction &Fill, raw_pwrite_stream &AsmStreamm,
- const BenchmarkKey &Key,
- bool GenerateMemoryInstructions);
+ const BenchmarkKey &Key, bool GenerateMemoryInstructions,
+ bool UseDummyPerfCounters);
// Creates an ObjectFile in the format understood by the host.
// Note: the resulting object keeps a copy of Buffer so it can be discarded once
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
index 85375dec2a44c..ecaf92643b012 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
@@ -264,6 +264,32 @@ class SubProcessFunctionExecutorImpl
return FD;
}
+ Error sendSyncMessageThroughSocket(int SocketFd) const {
+ char ToSend = 'a';
+
+ ssize_t BytesWritten = write(SocketFd, &ToSend, sizeof(char));
+
+ if (BytesWritten < 0)
+ return make_error<Failure>(
+ "Failed to write synchronization message to socket: " +
+ Twine(strerror(errno)));
+
+ return Error::success();
+ }
+
+ Error recieveSyncMessageFromSocket(int SocketFD) const {
+ char Buffer = 'b';
+
+ ssize_t BytesRecieved = read(SocketFD, &Buffer, sizeof(char));
+
+ if (BytesRecieved < 0)
+ return make_error<Failure>(
+ "Failed to read synchronization message from socket: " +
+ Twine(strerror(errno)));
+
+ return Error::success();
+ }
+
Error createSubProcessAndRunBenchmark(
StringRef CounterName, SmallVectorImpl<int64_t> &CounterValues) const {
int PipeFiles[2];
@@ -316,8 +342,9 @@ class SubProcessFunctionExecutorImpl
close(PipeFiles[0]);
// Make sure to attach to the process (and wait for the sigstop to be
- // delivered and for the process to continue) before we write to the counter
- // file descriptor. Attaching to the process before writing to the socket
+ // delivered and for the process to continue) before we write the counter
+ // file descriptor or dummy synchronization message.
+ // Attaching to the process before writing to the socket
// ensures that the subprocess at most has blocked on the read call. If we
// attach afterwards, the subprocess might exit before we get to the attach
// call due to effects like scheduler contention, introducing transient
@@ -337,12 +364,20 @@ class SubProcessFunctionExecutorImpl
"Failed to continue execution of the child process: " +
Twine(strerror(errno)));
- int CounterFileDescriptor = Counter->getFileDescriptor();
- Error SendError =
- sendFileDescriptorThroughSocket(PipeFiles[1], CounterFileDescriptor);
+ if (!State.usingDummyPerfCounters()) {
+ int CounterFileDescriptor = Counter->getFileDescriptor();
+ Error SendError =
+ sendFileDescriptorThroughSocket(PipeFiles[1], CounterFileDescriptor);
+
+ if (SendError)
+ return SendError;
- if (SendError)
- return SendError;
+ } else {
+ Error SendError = sendSyncMessageThroughSocket(PipeFiles[1]);
+
+ if (SendError)
+ return SendError;
+ }
int ChildStatus;
if (wait(&ChildStatus) == -1) {
@@ -383,13 +418,23 @@ class SubProcessFunctionExecutorImpl
// The following occurs within the benchmarking subprocess
pid_t ParentPID = getppid();
- Expected<int> CounterFileDescriptorOrError =
- getFileDescriptorFromSocket(Pipe);
+ int CounterFileDescriptor = 0;
+
+ if (!State.usingDummyPerfCounters()) {
+ Expected<int> CounterFileDescriptorOrError =
+ getFileDescriptorFromSocket(Pipe);
- if (!CounterFileDescriptorOrError)
- exit(ChildProcessExitCodeE::CounterFDReadFailed);
+ if (!CounterFileDescriptorOrError)
+ exit(ChildProcessExitCodeE::CounterFDReadFailed);
- int CounterFileDescriptor = *CounterFileDescriptorOrError;
+ CounterFileDescriptor = *CounterFileDescriptorOrError;
+
+ } else {
+ Error PossibleRecvError = recieveSyncMessageFromSocket(Pipe);
+
+ if (PossibleRecvError)
+ exit(ChildProcessExitCodeE::CounterFDReadFailed);
+ }
// Glibc versions greater than 2.35 automatically call rseq during
// initialization. Unmapping the region that glibc sets up for this causes
@@ -458,7 +503,8 @@ Expected<SmallString<0>> BenchmarkRunner::assembleSnippet(
BC.Key.RegisterInitialValues,
Repetitor.Repeat(Instructions, MinInstructions, LoopBodySize,
GenerateMemoryInstructions),
- OS, BC.Key, GenerateMemoryInstructions)) {
+ OS, BC.Key, GenerateMemoryInstructions,
+ State.usingDummyPerfCounters())) {
return std::move(E);
}
return Buffer;
diff --git a/llvm/tools/llvm-exegesis/lib/LlvmState.cpp b/llvm/tools/llvm-exegesis/lib/LlvmState.cpp
index 8aeea456fba1f..00a4b3fbf3685 100644
--- a/llvm/tools/llvm-exegesis/lib/LlvmState.cpp
+++ b/llvm/tools/llvm-exegesis/lib/LlvmState.cpp
@@ -76,14 +76,16 @@ Expected<LLVMState> LLVMState::Create(std::string TripleName,
const PfmCountersInfo &PCI = UseDummyPerfCounters
? ET->getDummyPfmCounters()
: ET->getPfmCounters(CpuName);
- return LLVMState(std::move(TM), ET, &PCI);
+ return LLVMState(std::move(TM), ET, &PCI, UseDummyPerfCounters);
}
LLVMState::LLVMState(std::unique_ptr<const TargetMachine> TM,
- const ExegesisTarget *ET, const PfmCountersInfo *PCI)
+ const ExegesisTarget *ET, const PfmCountersInfo *PCI,
+ bool UseDummyPerfCounters_)
: TheExegesisTarget(ET), TheTargetMachine(std::move(TM)), PfmCounters(PCI),
OpcodeNameToOpcodeIdxMapping(createOpcodeNameToOpcodeIdxMapping()),
- RegNameToRegNoMapping(createRegNameToRegNoMapping()) {
+ RegNameToRegNoMapping(createRegNameToRegNoMapping()),
+ UseDummyPerfCounters(UseDummyPerfCounters_) {
BitVector ReservedRegs = getFunctionReservedRegs(getTargetMachine());
for (const unsigned Reg : TheExegesisTarget->getUnavailableRegisters())
ReservedRegs.set(Reg);
diff --git a/llvm/tools/llvm-exegesis/lib/LlvmState.h b/llvm/tools/llvm-exegesis/lib/LlvmState.h
index 16f0def518256..751b24c98304b 100644
--- a/llvm/tools/llvm-exegesis/lib/LlvmState.h
+++ b/llvm/tools/llvm-exegesis/lib/LlvmState.h
@@ -80,6 +80,8 @@ class LLVMState {
return *RegNameToRegNoMapping;
}
+ bool usingDummyPerfCounters() const { return UseDummyPerfCounters; }
+
private:
std::unique_ptr<const DenseMap<StringRef, unsigned>>
createOpcodeNameToOpcodeIdxMapping() const;
@@ -88,7 +90,7 @@ class LLVMState {
createRegNameToRegNoMapping() const;
LLVMState(std::unique_ptr<const TargetMachine> TM, const ExegesisTarget *ET,
- const PfmCountersInfo *PCI);
+ const PfmCountersInfo *PCI, bool UseDummyPerfCounters_);
const ExegesisTarget *TheExegesisTarget;
std::unique_ptr<const TargetMachine> TheTargetMachine;
@@ -98,6 +100,8 @@ class LLVMState {
std::unique_ptr<const DenseMap<StringRef, unsigned>>
OpcodeNameToOpcodeIdxMapping;
std::unique_ptr<const DenseMap<StringRef, unsigned>> RegNameToRegNoMapping;
+
+ const bool UseDummyPerfCounters;
};
} // namespace exegesis
diff --git a/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp b/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
index 636dd11ff3265..dd7cdf2ad345e 100644
--- a/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
+++ b/llvm/tools/llvm-exegesis/lib/SnippetRepetitor.cpp
@@ -38,7 +38,8 @@ class DuplicateSnippetRepetitor : public SnippetRepetitor {
Entry.addInstruction(Instructions[I % Instructions.size()]);
}
}
- Entry.addReturn(State.getExegesisTarget(), CleanupMemory);
+ Entry.addReturn(State.getExegesisTarget(), CleanupMemory,
+ State.usingDummyPerfCounters());
};
}
@@ -70,7 +71,8 @@ class LoopSnippetRepetitor : public SnippetRepetitor {
const MCInstrDesc &MCID = Filler.MCII->get(Opcode);
if (!MCID.isTerminator())
continue;
- Entry.addReturn(State.getExegesisTarget(), CleanupMemory);
+ Entry.addReturn(State.getExegesisTarget(), CleanupMemory,
+ State.usingDummyPerfCounters());
return;
}
@@ -115,7 +117,8 @@ class LoopSnippetRepetitor : public SnippetRepetitor {
// Set up the exit basic block.
Loop.MBB->addSuccessor(Exit.MBB, BranchProbability::getZero());
- Exit.addReturn(State.getExegesisTarget(), CleanupMemory);
+ Exit.addReturn(State.getExegesisTarget(), CleanupMemory,
+ State.usingDummyPerfCounters());
};
}
diff --git a/llvm/tools/llvm-exegesis/llvm-exegesis.cpp b/llvm/tools/llvm-exegesis/llvm-exegesis.cpp
index 261335a817d06..a18226fafd2ab 100644
--- a/llvm/tools/llvm-exegesis/llvm-exegesis.cpp
+++ b/llvm/tools/llvm-exegesis/llvm-exegesis.cpp
@@ -477,11 +477,6 @@ void benchmarkMain() {
if (BenchmarkPhaseSelector == BenchmarkPhaseSelectorE::Measure)
ExitOnErr(State.getExegesisTarget().checkFeatureSupport());
- if (ExecutionMode == BenchmarkRunner::ExecutionModeE::SubProcess &&
- UseDummyPerfCounters)
- ExitWithError("Dummy perf counters are not supported in the subprocess "
- "execution mode.");
-
const std::unique_ptr<BenchmarkRunner> Runner =
ExitOnErr(State.getExegesisTarget().createBenchmarkRunner(
BenchmarkMode, State, BenchmarkPhaseSelector, ExecutionMode,
diff --git a/llvm/unittests/tools/llvm-exegesis/Common/AssemblerUtils.h b/llvm/unittests/tools/llvm-exegesis/Common/AssemblerUtils.h
index 2804a6e69e824..36be02bf68a92 100644
--- a/llvm/unittests/tools/llvm-exegesis/Common/AssemblerUtils.h
+++ b/llvm/unittests/tools/llvm-exegesis/Common/AssemblerUtils.h
@@ -82,7 +82,7 @@ class MachineFunctionGeneratorBaseTest : public ::testing::Test {
Key.RegisterInitialValues = RegisterInitialValues;
EXPECT_FALSE(assembleToStream(*ET, createTargetMachine(), /*LiveIns=*/{},
RegisterInitialValues, Fill, AsmStream, Key,
- false));
+ false, false));
Expected<ExecutableFunction> ExecFunc = ExecutableFunction::create(
createTargetMachine(), getObjectFromBuffer(AsmStream.str()));
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