Misprediction penalty
Beginner
The time lost when the processor guesses an “if” wrong and has to throw away work and start again.
Novice
The clock cycles lost when a branch prediction turns out wrong: the wrong-path work is discarded and the pipeline refills from the right instruction. On recent desktop and server cores it is roughly 10 to 25 cycles.
Expert
Roughly the fetch-to-resolve depth, plus however long the branch waited for its operands. Added CPI ≈ branches per instruction × mispredict rate × penalty, and each lost cycle costs W issue slots on a W-wide core.
Explained in Branch prediction and out-of-order execution (Architectures).
See also: Branch prediction, CPI (cycles per instruction).