hot spot

1. (primarily used by C/Unix programmers, but spreading)

It is received wisdom that in most programs, less than 10% of

the code eats 90% of the execution time; if one were to graph

instruction visits versus code addresses, one would typically

see a few huge spikes amidst a lot of low-level noise. Such

spikes are called "hot spots" and are good candidates for

heavy optimisation or hand-hacking. The term is especially

used of tight loops and recursions in the code's central

algorithm, as opposed to (say) initial set-up costs or large

but infrequent I/O operations.

See tune, bum, hand-hacking.

2. The active location of a cursor on a bit-map display. "Put

the mouse's hot spot on the "ON" widget and click the left

button."

3. A screen region that is sensitive to mouse clicks, which

trigger some action. Hypertext help screens are an example,

in which a hot spot exists in the vicinity of any word for

which additional material is available.

4. In a massively parallel computer with shared memory,

the one location that all 10,000 processors are trying to read

or write at once (perhaps because they are all doing a

busy-wait on the same lock).

5. More generally, any place in a hardware design that turns

into a performance bottleneck due to resource contention.

[Jargon File]

(1995-02-16)