MIT 6.004 Spring 2020
Reminder: Pipelining with Data
Hazards
§ Strategy 1: Stall. Wait for the result to be available
by freezing earlier pipeline stages
§ Simple, wastes cycles, higher CPI
§ Strategy 2: Bypass. Route data to the earlier
pipeline stage as soon as it is calculated
§ More expensive, lower CPI
§ Still needs stalls when result is produced after EXE stage
§ Can trade off having fewer bypasses with stalling more
often
April 28, 2020 L19-3
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