Pipelining

Question 1

Simple pipeline stages

Answer 1

Fetch, decode, execute, memory, writeback

Question 2

In-order pipeline

Answer 2

when instructions go through the execute stage in program order

Question 3

Data hazard

Answer 3

RAW, WAR, WAW. When two instructions are accessing the same value or address. Error caused by data dependencies.

Question 4

Control hazard

Answer 4

when the execution of one instruction determines if another instruction is executed or not. (taken/not taken).

let’s say a program doesn’t run in sequential order of its instructions. Now what?

Question 5

Dependency vs hazard

Answer 5

dependency is how two instructions are related, hazard is the problem or wrong execution that arises when two instructions are dependent.

Question 6

Data stall vs propagated stall

Answer 6

data stall is when an instruction waits to enter a stage to avoid a data hazard. Propagated stall is when an instruction can’t fetch because the previous instruction has not executed yet.

Question 7

Bypassing/Forwarding

Answer 7

forwarding data directly to the input port to the stage it is used. Like execution, memory or writeback.

Question 8

Control Speculation

Answer 8

predict the result of a branch instruction. (taken/ not taken?)