Performance engineering, profilers, and seeing the invisible

Nelson Elhage · 18 Dec 2023

Nelson Elhage did not write this page.

Every claim below was made in this piece, quoted word for word and numbered in the order the piece makes them, so you can read it there rather than take our word for it. The sentence above each quote is our reading of the claim, not their wording. Each quote was checked against a stored copy of the page at build time; where the two differ, the quote is the fact.

Our reading
Profilers show where time is spent but not which of that time can feasibly be reduced or is worth optimizing.
Mental modelThe map is not the territory

Their wordsProfilers can only show you "what is there"; skillful performance engineering requires understanding the information that shapes and informs the profile but is "not there" in the profile itself.
Our reading
A profiler measures time already spent in an operation, not how much time would be saved by optimizing it.

Their wordsa profile tells you how much time a program spent in a given operation; but not how much time it would spend if you optimized that operation.

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