Performance tracing facility for clangd.
Summary:
This lets you visualize clangd's activity on different threads over time,
and understand critical paths of requests and object lifetimes.
The data produced can be visualized in Chrome (at chrome://tracing), or
in a standalone copy of catapult (http://github.com/catapult-project/catapult)
This patch consists of:
- a command line flag "-trace" that causes clangd to emit JSON trace data
- an API (in Trace.h) allowing clangd code to easily add events to the stream
- several initial uses of this API to capture JSON-RPC requests, builds, logs
Example result: https://photos.app.goo.gl/12L9swaz5REGQ1rm1
Caveats:
- JSON serialization is ad-hoc (isn't it everywhere?) so the API is
limited to naming events rather than attaching arbitrary metadata.
I'd like to fix this (I think we could use a JSON-object abstraction).
- The recording is very naive: events are written immediately by
locking a mutex. Contention on the mutex might disturb performance.
- For now it just traces instants or spans on the current thread.
There are other things that make sense to show (cross-thread flows,
non-thread resources such as ASTs). But we have to start somewhere.
Reviewers: ioeric, ilya-biryukov
Subscribers: cfe-commits, mgorny
Differential Revision: https://reviews.llvm.org/D39086
llvm-svn: 317193
diff --git a/clang-tools-extra/clangd/tool/ClangdMain.cpp b/clang-tools-extra/clangd/tool/ClangdMain.cpp
index 420ef3a..2808d05 100644
--- a/clang-tools-extra/clangd/tool/ClangdMain.cpp
+++ b/clang-tools-extra/clangd/tool/ClangdMain.cpp
@@ -10,6 +10,7 @@
#include "ClangdLSPServer.h"
#include "JSONRPCDispatcher.h"
#include "Path.h"
+#include "Trace.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Path.h"
@@ -56,6 +57,12 @@
"Mirror all LSP input to the specified file. Useful for debugging."),
llvm::cl::init(""), llvm::cl::Hidden);
+static llvm::cl::opt<Path> TraceFile(
+ "trace",
+ llvm::cl::desc(
+ "Trace internal events and timestamps in chrome://tracing JSON format"),
+ llvm::cl::init(""), llvm::cl::Hidden);
+
int main(int argc, char *argv[]) {
llvm::cl::ParseCommandLineOptions(argc, argv, "clangd");
@@ -81,6 +88,18 @@
<< EC.message();
}
}
+ llvm::Optional<llvm::raw_fd_ostream> TraceStream;
+ std::unique_ptr<trace::Session> TraceSession;
+ if (!TraceFile.empty()) {
+ std::error_code EC;
+ TraceStream.emplace(TraceFile, /*ref*/ EC, llvm::sys::fs::F_RW);
+ if (EC) {
+ TraceFile.reset();
+ llvm::errs() << "Error while opening trace file: " << EC.message();
+ } else {
+ TraceSession = trace::Session::create(*TraceStream);
+ }
+ }
llvm::raw_ostream &Outs = llvm::outs();
llvm::raw_ostream &Logs = llvm::errs();
@@ -113,7 +132,7 @@
// Initialize and run ClangdLSPServer.
ClangdLSPServer LSPServer(Out, WorkerThreadsCount, EnableSnippets,
ResourceDirRef, CompileCommandsDirPath);
-
constexpr int NoShutdownRequestErrorCode = 1;
+ llvm::set_thread_name("clangd.main");
return LSPServer.run(std::cin) ? 0 : NoShutdownRequestErrorCode;
}