16 Pipelining

Question 1

Stages of the fetch-execute cycle?

Answer 1

Question 2

What is pipelining?

Answer 2

Pipelining is an implementation technique in which multiple tasks are executed simultaneously

Question 3

Analogous to single-cycle datapath diagram?

Answer 3

Question 4

Analogous to pipelined datapath diagram?

Answer 4

Question 5

Pipelining performs stages concurrently.

Latency and Throughput changes of pipelining?

Answer 5

Latency The elapsed time from the start to the finish of a task. Latency is NOT improved by pipelining.

Throughput Number of instructions performed per unit of time. Pipelining IMPROVES the throughput.

Question 6

Single-cycle datapath

Answer 6

Question 7

Pipelined datapath

Answer 7

Question 8

Latency

Answer 8

This is the elapsed time from start to finish of a particular instruction

Question 9

Throughput

Answer 9

How many instructions can be completed per unit of time (usually a number of cycles)

Question 10

Pipelining only improves ….

Answer 10

Pipelining only improves throughput

It doesn’t make the processor faster

It does allow more instructions to be completed within a window of time

Question 11

Pipelining delay problems?

Answer 11

Then, the microprocessor needs to WAIT!

If the instructions MUST be completed in the correct order, then we need to wait for longer instructions to complete, e.g., Instruction 3 takes 2 cycles => need to wait

Question 12

But what if we don’t need to wait (no data dependencies)?

Answer 12

• We can therefore carry out instructions “out of order” o In other words, if we are ready to go, then GO
• BUT, only if we don’t need to wait for a previous instruction to supply relevant data
• AND, we might need to wait later on when the data DOES become important/relevant
• This requires knowledge of the program flow

Question 13

Single-cycle or non-pipelined processor?

Answer 13

Question 14

Pipelined processor

Answer 14

Question 15

Additions made to a pipelined processor?

Answer 15