5.5.4 Performance Flame Graph

Introduction

A flame graph is a graphical way to display performance data collected by tools such as perf. It aggregates and analyzes the data to help identify performance hotspots.

Each box in a flame graph represents a function. The width of a box represents its execution time, so wider functions take longer to execute.

Each level higher in the flame graph represents a deeper function call. The top-level functions are leaf functions.

Code repository: (https://github.com/brendangregg/FlameGraph.git)

Supported Platforms

Platform	Runtime Environment
RDK X3, RDK X3 Module, RDK X5, RDK X5 Module	Ubuntu 20.04 (Foxy), Ubuntu 22.04 (Humble)

Preparation

RDK Platform

1. The flame graph tool consists of two parts. The first part is the perf executable. perf is a software performance analysis tool used to collect and output function call statistics for the system or a specific process. The RDK operating system already includes perf, so you can use it directly.

2. The second part of the flame graph tool is a script that parses perf text output. The script parses the text data collected by perf and generates an SVG function call flame graph for easy observation and analysis.

Usage

1. Use the perf record tool to sample function calls on the RDK system and generate a perf.data file.

   root@ubuntu:~# perf record -F 99 -a -g -- sleep 60

2. Use perf script to parse the perf.data file and generate out.perf.

   root@ubuntu:~# perf script > out.perf

3. On a PC or RDK, run git clone https://github.com/brendangregg/FlameGraph.git, enter the flamegraph directory, and copy the out.perf file generated in step 2 into the flamegraph directory. Use stackcollapse-perf.pl from the flame graph tool package to collapse out.perf into out.folded.

   ./stackcollapse-perf.pl out.perf > out.folded

4. Use flamegraph.pl to generate an SVG flame graph.

   ./flamegraph.pl out.folded > flame.svg

Steps 1 and 2 are performed on the RDK. Steps 3 and 4 can be performed on a PC or RDK.

Result Analysis

After following the workflow in the previous section, the function calls recorded on the RDK system are shown below.