The baseline execution time of a program on a 2 GHz single core machine is 100 nanoseconds (ns). The code corresponding to 90% of the execution time can be fully parallelized. The overhead for using an additional core is 10 ns when running on a multicore system. Assume that all cores in the multicore system run their share of the parallelized code for an equal amount of time.
$$ \text { The number of cores that minimize the execution time of the program is _______. } $$A processor X1 operating at 2 GHz has a standard 5-stage RISC instruction pipeline having a base CPI (cycles per instruction) of one without any pipeline hazards. For a given program P that has 30% branch instructions, control hazards incur 2 cycles stall for every branch. A new version of the processor X2 operating at same clock frequency has an additional branch predictor unit (BPU) that completely eliminates stalls for correctly predicted branches. There is neither any savings nor any additional stalls for wrong predictions. There are no structural hazards and data hazards for X1 and X2. If the BPU has a prediction accuracy of 80%, the speed up (rounded off to two decimal places) obtained by X2 over X1 in executing P is ____________.
A five-stage pipeline has stage delays of 150, 120, 150, 160 and 140 nanoseconds. The registers that are used between the pipeline stages have a delay of 5 nanoseconds each.
The total time to execute 100 independent instructions on this pipeline, assuming there are no pipeline stalls, is ______ nanoseconds.
Consider the following instruction sequence where register R1, R2 and R3 are general purpose and MEMORY[X] denotes the content at the memory location X.
Instruction |
Semantics |
Instruction Size (bytes) |
MOV R1, (5000) |
R1 ← MEMORY[5000] |
4 |
MOV R2, (R3) |
R2 ← MEMORY[R3] |
4 |
ADD R2, R1 |
R2 ← R1 + R2 |
2 |
MOV (R3), R2 |
MEMORY[R3] ← R2 |
4 |
INC R3 |
R3 ← R3 + 1 |
2 |
DEC R1 |
R1 ← R1 – 1 |
2 |
BNZ 1004 |
Branch if not zero to the given absolute address |
2 |
HALT |
Stop |
1 |
Assume that the content of the memory location 5000 is 10, and the content of the register R3 is 3000. The content of each of the memory locations from 3000 to 3010 is 50. The instruction sequence starts from the memory location 1000. All the numbers are in decimal format. Assume that the memory is byte addressable.
After the execution of the program, the content of memory location 3010 is ______