Wednesday, April 16, 2008

The smallwig theory of optimization

There are three kinds of optimization.
  1. Optimization by using a more sensible overall approach.
  2. Optimization by making the code less weird.
  3. Optimization by making the code more weird.
You've probably heard, and maybe even spouted yourself, the phrase "premature optimization is the root of all evil." It's exclusively "Type 3 optimization" that this aphorism applies to. Types 1 and 2 are quite fine to engage in pre-emptively.

To make a type 3 optimization, your burdens are six:
  1. Thou shalt have excellent, comprehensive unit tests.
  2. Thou shalt have a reliable benchmark, based on representative inputs.
  3. Thou shalt demonstrate that your change improves the benchmark.
  4. Thou shalt successfully argue that this improvement really matters.
  5. Thou shalt comment the code.
  6. In nontrivial cases, thou shalt also preserve the clear-but-slow implementation, to use in parity tests with your optimized implementation.
In all things, remember these truths:
  1. Your brain is a terrible profiler.
  2. Hotspot will outsmart you.
  3. It just doesn't matter, until it matters.
If you believe this post, please spread the word!


Fatih Co┼čkun said...

I believe; starred.

Unknown said...

The remedy for premature optimization is to expedite knowledge.

Elliotte Rusty Harold said...

I'd argue that #1 and #2 aren't really optimizations at all. Using a more sensible approach and/or making the code less weird are benefits in and of themselves, irrespective of their effect on performance. They are things you would do even if they made the code slower, and refusing to do them when they make the code slower is a case of premature optimization. Of course if they do make the code faster (and they usually do) then so much the better; and even if they don't make the code faster immediately, these sorts of improvements usually make the code more amenable to carefully planned out, non-premature optimization later.

Elliotte Rusty Harold said...

Also, what about option 2.5? Optimization that neither makes the code less nor more weird, simply different? My gut is that that is premature, if or no other reason that it wastes time that could be spent elsewhere.

Jim Xochellis said...

Very nice and useful!

Personally, I am very interesting to find out what is really happening in the real word nowadays. Do the professional programmers of our generation optimize too late or too early? What is most frequent?

Do you happen to know any surveys
or polls which can provide objective information regarding the way the programmers use to optimize nowadays?

Thank you very much,
Jim Xochellis


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