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lua-perf

cn

lua-perf is a performance profiling tool implemented based on eBPF, supporting Lua 5.3, Lua 5.4, and Lua 5.5.

Features

  • Provides performance analysis for mixed C and Lua code, as well as pure C code.
  • Uses stack sampling technique with minimal performance impact on the target process, making it suitable for production environments.
  • Performs stack backtracing in the kernel space using eh-frame, eliminating the need for the target process to use the -fno-omit-frame-pointer option to preserve stack frame pointers.
  • Automatically detects the Lua version of the target process, no manual specification required.
  • Precisely locates the L variable position via DWARF debug information, supporting GCC/Clang O0~O3 optimization levels.

Requirements

To use lua-perf, make sure you meet the following requirements:

  • The installed kernel version needs to be 5.17 or above.

Generating Flame Graphs

To generate flame graphs, you need to use lua-perf in conjunction with the FlameGraph tool. Here's how you can do it:

  1. First, run the command sudo lua-perf -p <pid> -f <HZ> to sample the call stacks of the target process and generate a perf.fold file in the current directory. <pid> is the process ID of the target process, which can be a process inside a Docker container or a process on the host machine. <HZ> is the stack sampling frequency, with a default value of 100 (100 samples per second).

  2. Next, convert the perf.fold file to a flame graph by running ./FlameGraph/flamegraph.pl perf.folded > perf.svg.

  3. Finally, you will find the generated flame graph, perf.svg, in the current directory.

Here's an example flame graph:

perf

Logging

In the BPF program, bpf_trace_printk is used to print logs. If you suspect any abnormalities in the performance sampling, you can view the logs using the following commands:

sudo mount -t tracefs nodev /sys/kernel/tracing
sudo cat /sys/kernel/debug/tracing/trace_pipe

Known Issues

lua-perf currently has the following known issues:

  • Lack of support for CFA_expression, which may result in failed stack backtracing in extreme cases.
  • The analysis of CFA instructions does not handle vdso at the moment, causing stack backtracing failures for function calls in vdso.
  • The process of merging C stacks and Lua stacks uses a heuristic strategy, which may have some flaws in extreme cases (none have been found so far).

Future Work

The following tasks are planned for lua-perf:

  • Support for CFA_expression
  • Support for vdso
  • Optimization of the merging strategy for C stacks and Lua stacks