It is often possible to sacrifice some speed in a circuit in order to reduce its energy consumption. Assume that we can reduce energy consumption by a factor of X (new energy is 1/X times the old energy) when we increase the latency by a factor of X (new latency is X times the old latency). Using this tradeoff, we can adjust latencies of pipeline stages to minimize energy consumption without sacrificing any performance. Repeat 4.39.2 for this adjusted processor.

Exercise 4.39.2

What is the power dissipated in watts (joules per second)?

Problems in this exercise assume that, during an execution of the program, processor cycles are spent in the following way. A cycle is "spent" on an instruction if the processor completes that type of instruction in that cycle; a cycle is "spent" on a stall if the processor could not complete an instruction in that cycle because of a stall.

Problems in this exercise also assume that individual pipeline stages have the following latency and energy consumption. The stage expends this energy in order to do its work within the given latency. Note that no energy is spent in the MEM stage during a cycle in which there is no memory access. Similarly, no energy is spent in the WB stage in a cycle in which there is no register write. In several of the following problems, we make assumptions about how energy consumption changes if a stage performs its work slower or faster than this.

a. b. ADD 25% 25% BEQ 20% 10% LW 20% 25% SW 10% 20% Control Stalls 10% 10% Data Stalls 15% 10%