Notes on  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 optimization 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, 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 gestures, which trigger
some action. World Wide Web pages now provide the CANONICAL
examples; WWW browsers present hypertext links as hot spots which,
when clicked on, point the browser at another document (these are
specifically called HOTLINKs).

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.

J3N Research Labs

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