Performance tracing facility for clangd.

Description

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

Details

Committed
sammccallNov 2 2017, 2:21 AM
Differential Revision
D39086: Performance tracing facility for clangd.
Parents
rL317192: Fix building for ARM with dwarf exception handling
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