Google Summer of Code 2016

This summer, I was selected for the prestigious Google Summer of Code program with the Performance Co-Pilot organization. Performance Co-Pilot is an open source system level performance analysis and inference toolkit. It has an agent based architecture, where different agents (called Performance Metric Domain Agents or PMDAs) are responsible for collecting performance metrics. Each agent reports the collected metrics to a daemon, called the Performance Metric Collection Daemon, or PMCD for short. Clients wanting to access metrics can then send a request to PMCDs with the appropriate request parameters. PCP has a set of client tools, pmval, pmlogger, pminfo, pmdumptext, pminfer… and so on that help users better understand the metrics reported by the collector daemon. PCP has an open API for building agents for any piece of software you want, and some ship with the toolkit itself, like linux, influxdb, mysql, elasticsearch… and so on.

Performance Co-Pilot also supports instrumentation, i.e. user applications reporting metrics at runtime, through the Memory Mapped Values (MMV) PMDA. The PMDA basically monitors memory mapped files and reports metrics by reading them to a PMCD, so we can run PCP client tools on them just as we would run them on a giant monolithic database application like mysql. The instrumentation API currently has implementations in C, with bindings for Perl and Python, and a separate application Parfait, implements the Java API. My project was to implement an instrumentation library for PCP in golang.

Go is a new and unique programming language built at Google. Its most appealing features are tiny language spec and easy concurrency. The language has gained immense popularity for its tooling and productivity oriented design and in recent times has gained widespread adoption and a lot of popular open source projects have been implemented in golang.

This post summarizes my 4 month program period in the summer of 2016 hacking on golang and instrumentation.

Community Bonding

Before the beginning of the official program period, Google allows students one month to get familiar with the organization they will contribute to, to get familiar with the programming practices, source code, get doubts cleared etc. PCP is a Red Hat project and is progress is essentially tracked using a wekan board that is also public at So at the beginning my mentors created a separate board for me to add tickets and track progress using them. We also used IRC using the #pcp-go channel on freenode to talk about progress. Finally, I was expected to send weekly reviews about progress achieved in that week and what I expected to achieve the following one. Needless to say this post is basically a concatenation of those reviews.

Week 1–2

Week 3

  • cloned parfait, the java project implementing instrumentation for PCP, and got it to build locally
  • set up a parfait-examples repo to track different APIs in parfait and their usage.

Week 4

  • read up on instrumentation in java, especially the instrument package and the premain method, and the corresponding implementation in parfait with parfait-agent
  • also tried to find examples of similar functionality in golang, came across expvar in golang with the `/var/debug` export, as well as davecheney/gmx and prometheus.

Program Period

The official program period began on May 23

Week 1

Week 2

  • I was moving this week so couldn’t work much on the project

Week 3

Week 4

Week 5–6

  • defined the PCPWriter type to write metric data to mmv files
  • defined a bytebuffer type that replicated behavior similar to Java ByteBuffer for a fixed size byte array
  • added a couple of basic examples on using the API
  • my mentor, Nathan Scott contributed an icon for the project

Week 7

Week 8–9

Week 10–11

Week 12


The current repository for the project is hosted at Installation and usage instructions are in the README, while there are also some basic examples in the `examples` subfolder. The current list of things being worked on can be seen by looking at the issues.