• Author / Uploaded
• Armando Miguel Tapia Meza

Citation preview

Workshop Week 8. Armando Miguel Tapia Meza

Consider the following loop. LOOP: ld x10, 0(x13) ld x11, 8(x13) add x12, x10, x11 subi x13, x13, 16 bnez x12, LOOP

Assume that perfect branch prediction is used (no stalls due to control hazards), that there are no delay slots, that the pipeline has full forwarding support, and that branches are resolved in the EX (as opposed to the ID) stage. ● ●

Show a pipeline execution diagram for the first two iterations of this loop. Mark pipeline stages that do not perform useful work. How often while the pipeline is full do we have a cycle in which all five pipeline stages are doing useful work? (Begin with the cycle during which the subi is in the IF stage. End with the cycle during which the bnezis in the IF stage.)

-) F–D–E–M-W F–D–E–M–W -----------------F–D–E–X-W F–D–E–X–W F–D–E–X–X F–D–E–M–W ----------------------F–D–E–M–W F–D–E–X-W F–D–E–X–W F–D–E–X–X -) 20%---40%---40%---60%---80%---80%---60%---80%---60%---80%---80%---80%---40%---40%---20%---20%

This exercise explores energy efficiency and its relationship with performance. Problems in this exercise assume the following energy consumption for activity in Instruction memory, Registers, and Data memory. You can assume that the other components of the datapath consume a negligible amount of energy. (“Register Read” and “Register Write” refer to the register file only.)

Assume that components in the datapath have the following latencies. You can assume that the other components of the datapath have negligible latencies.

● ●

How much energy is spent to execute an add instruction in a single-cycle design and in the five-stage pipelined design? What is the worst-case RISC-V instruction in terms of energy consumption? What is the energy spent to execute it? -) F 140 pj

D 140pj

E 0

M 0

W 60pj

Total 340PJ

F 140 pj

D 140pj

E 0

M 140pj

W 60pj

Total 480pj

-)