Contribution: Lock Contention Profiler for HotSpot

[Peter Hofer]

Hello everyone,

we are researchers at the University of Linz and have worked on a lock 
contention profiler that is built into HotSpot. We would like to 
contribute this work to the OpenJDK community.

Our profiler records an event when a thread fails to acquire a contended 
lock and also when a thread releases a contended lock. It further 
efficiently records the stack traces where these events occur. We 
devised a versatile visualization tool that analyzes the recorded events 
and determines when and where threads _cause_ contention by holding a 
contended lock. The visualization tool can show the contention by stack 
trace, by lock, by lock class, by thread, and by any combination of 
those aspects.

We described our profiler in more detail in a research paper at ICPE 
2016. [1] In our evaluation, we found that the overhead is typically 
below 10% for common multi-threaded Java benchmarks. Please find a free 
download of the paper on our website:
> http://mevss.jku.at/lct/

I contribute this work on behalf of Dynatrace Austria (the sponsor of 
this research), my colleagues David Gnedt and Andreas Schoergenhumer, 
and myself. The necessary OCAs have already been submitted.

We provide two patches:

Patch 1. A patch for OpenJDK 8u102-b14 with the profiler that we 
described and evaluated in our paper, plus minor improvements. It 
records events for Java intrinsic locks (monitors) and for 
java.util.concurrent locks (ReentrantLock and ReentrantReadWriteLock). 
We support only Linux on 64-bit x86 hardware.

> http://cr.openjdk.java.net/~tschatzl/phofer/webrev_hotspot_jdk8u102b14/
> http://cr.openjdk.java.net/~tschatzl/phofer/webrev_jdk_jdk8u102b14/

Patch 2. A patch for OpenJDK 9+140 with a profiler for VM-internal 
native locks only. We consider this to be useful for HotSpot developers 
to find locking bottlenecks in HotSpot itself. We tested this patch only 
on Linux on 64-bit x86 hardware, but it should require few changes for 
other platforms.

> http://cr.openjdk.java.net/~tschatzl/phofer/webrev_nativelocksonly_hotspot_jdk9%2b140/
> http://cr.openjdk.java.net/~tschatzl/phofer/webrev_nativelocksonly_jdk_jdk-9%2b140/

With both patches, the profiler is enabled with -XX:+EnableEventTracing. 
By default, an uncompressed event trace is written to file "output.trc".

More detailed usage information and a download of the corresponding 
visualization tool is available on our website, http://mevss.jku.at/lct/.

Kind regards,
  Peter Hofer


--
Peter Hofer
Christian Doppler Laboratory on Monitoring and Evolution of 
Very-Large-Scale Software Systems / Institute for System Software
University of Linz


[1] Peter Hofer, David Gnedt, Andreas Schoergenhumer, Hanspeter 
Moessenboeck. Efficient Tracing and Versatile Analysis of Lock 
Contention in Java Applications on the Virtual Machine Level. 
Proceedings of the 7th ACM/SPEC International Conference on Performance 
Engineering (ICPE’16), Delft, Netherlands, 2016.