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PerfJ

PerfJ is a wrapper of linux perf for java programs.

In order to profile java programs, you need a profiler that can sample stack traces. There has historically been two types of profilers:

System profilers: like Linux perf, which shows system code paths (eg, JVM GC, syscalls, TCP), but not Java methods.

JVM profilers: like hprof, LJP, and commercial profilers. These show Java methods, but usually not system code paths.

Ideally, we need a profile result that does it all: system and Java code paths. Apart from convenience, it also shows system code-paths in Java context, which can be crucial for understanding a profile properly.

The problem is getting a system profiler to understand Java methods and stack traces. If you try Linux perf_events, for example, you'll see hexadecimal numbers and broken stack traces, as it can't convert addresses into Java symbols, and can't walk the JVM stack.

There are two specific problems:

The JVM compiles methods on the fly (just-in-time: JIT), and doesn't expose a traditional symbol table for system profilers to read.

The JVM also uses the frame pointer register (RBP on x86-64) as a general purpose register, breaking traditional stack walking.

Thanks to the work by Brendan Gregg and Zoltan Majo. We will have an option to turn on the preservation of frame pointer on JDK 8u60+.

This project is based on Johannes Rudolph's work at here, but PerfJ is more convenient and safer to use.

PerfJ can produce flame graph through Brendan Gregg's FlameGraph tool .

Below is an example shows the hotspot of a pure java leveldb program. Green is Java layer, yellow is JVM layer, and red is system layer(native user-level, or kernel). Longer bar means higher cpu percentage.

PerfJ CPU Flame Graph Example

There is a raw interactive SVG image [here] (http://blog.minzhou.info/perfj/perfj.svg).

Prerequisites

Linux x86_64
perf
JDK 8u60 and higher

Build

Before starting building PerfJ, make sure gcc is already installed.

checkout the source from github

git clone https://github.com/coderplay/perfj.git

and run below in the future building

cd perfj
./gradlew releaseTarGz

Installation

Before install PerfJ, you should install Linux perf first

To install perf on centos/redhat/fedora linux system

yum install perf.x86_64

To install perf on ubuntu linux system

apt-get install linux-tools-common linux-tools-generic linux-tools-`uname -r`

then download perfj-*.tgz from the [release page] (https://github.com/coderplay/perfj/releases), untar it

tar zxvf perf-*.tgz

Usage

Check the [wiki pages] (https://github.com/coderplay/perfj/wiki)

License

This library is licensed under GPLv2. See the LICENSE file.