The Unreasonable Effectiveness of Tuning

The Unreasonable Effectiveness of Tuning

Grand Ballroom - Salon A/B/C/D

Counter-intuitively, the effects of tuning (tweaks to a system in response to real workloads) often dominate the effects of fundamentally better technology. Well-tuned, bad systems usually outperform less mature, better systems.


In this talk, Facebook’s Keith Adams, co-founder of HHVM, the runtime which powers the largest website in the world, will cover:

  • The evidence base: examples where well-tuned incumbents outperformed better, but less mature designs, in both hardware and software
  • The tragedy: how our ignorance of this effect limits technical progress
  • Challenges for planning complex technical projects

    One of the examples covered will be Facebook’s HipHop Virtual Machine, which was 7x slower than its performance target at the start. Today, it is 2x faster than that original goal. Yet the block-diagram level design of the system is unchanged. There have been no research breakthroughs, conceptual insights, or heroic ground-up rewrites. The 14x difference came instead from tuning: HHVM now does thousands of small things slightly better.

    keith.adams's picture
    Keith Adams is a founding member of Facebook's HipHop Virtual Machine (HHVM) team. HHVM is a Facebook's just-in-time compiler for PHP. Keith has also contributed to Facebook's search engine. Before Facebook, he worked on VMware's virtual machine monitor. He's a founding member of the I-can't-believe-I'm-a-PHP-advocate club.