CSCE614 Computer Architecture (Spring 2012)
Assignment #1
Due: 2/13(Mon) 2:50PM
1. A new faster machine is being announced. According to the announcement, the old machine and new
machine have the following specs:
A. The old machine: Clock rate of 2 GHz
Instruction
Class
A
B
C
D
B. The new machine: Clock rate of 2.5 GHz
CPI
Frequency
2
3
3
8
45 %
30 %
20 %
5%
Instruction
Class
A
B
C
D
CPI
Frequency
2
2
3
5
35 %
30 %
25 %
10 %
(a) What is the CPI for each computer?
(b) What are the native MIPS ratings for those two machines?
MIPS =
Instruction Count
106 ∗ Execution Time
(c) What is the speedup of the new machine?
2. Suppose we enhance a computer to make all floating-point instructions run 7 times faster. Let’s look at
how speedup behaves when we incorporate the faster floating-point hardware. If the execution time of
some benchmark before the floating-point enhancement is 15 seconds, what will the speedup be if 35% of
the 15 seconds is spent executing floating-point instructions?
3. When making changes to optimize part of a processor, it is often the case that speeding up one type of
instruction comes at the cost of slowing down something else. For example, if we put in a complicated
fast floating-point unit, that takes space, and something might have to be moved farther away from the
middle to accommodate it, adding an extra cycle in delay to reach that unit. The basic Amdahl’s law
equation does not take this trade-off into account.
(a) If the new fast floating-point unit speeds up floating-point operations by 2 times, and the operations
takes 20% of the original program’s execution time, what is the overall speedup (ignoring the penalty to
any other instructions)?
(b) Now assume that speeding up the floating-point unit slowed down data cache access, resulting in a 1.5
times slowdown. Data cache accesses consume 10% of the total execution time. What is the overall
speedup now?
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4. The main reliability measure is mean time to failure (MTTF), and design decisions affect their
reliability.
(a) We have a single processor with a failures in time (FIT) of 100. What is the MTTF for this system?
(b) If it takes 2 days to get the system running again, what is the availability of the system?
5. Your company has just bought a new Intel Core i5 dual-core processor, and you have been tasked with
optimizing your software for this processor. You will run two applications on this system, but the
resource requirements are not equal. The first application needs 80% of the resources, and the other only
20% of the resources.
(a) Given that 40% of the first application is parallelizable, how much speedup would you achieve with
that application if run in isolation?
(b) Given that 99% of the second application is parallelizable, how much speedup would this application
observe if run in isolation?
(c) Given that 60% of the first application is parallelizable, how much overall system speedup
would you observe if you parallelized it, but not the second application?
(d) How much overall system speedup would you achieve if you parallelize both applications?
6. We have a program of 103 instructions in the format of “lw, add, lw, add, …” The add instruction only
depends on the lw instruction right before it. The lw instruction also only depends on the add instruction
right before it. If the program is executed on the pipelined datapath of Figure 1,
(a) What would be the actual CPI?
(b) Without forwarding, what would be the actual CPI?
7. Consider executing the following code on the pipelined datapath of Figure 1.
add
sub
add
add
add
$2,
$4,
$5,
$7,
$8,
$3,
$3,
$3,
$6,
$2,
$1
$5
$7
$1
$6
At the end of the fifth cycle of execution, which registers are being read and which register will be written?
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Figure 1. Pipelined Datapath
8. Your colleague at Intel suggests that, since the yield is so poor, you might make chips cheaper if you
placed an extra core on the die and only threw out chips on which both processors had failed. We will
solve this exercise by viewing the yield as a probability of no defects occurring in a certain area given the
defect rate. Calculate probabilities based on each Intel Core i5 core separately (this may not be entirely
accurate, since the yield equation is based on empirical evidence rather than a mathematical calculation
relating the probabilities of finding errors in different portions of the chip).
(a) What is the probability that a defect will occur on no more than one of the two processor cores?
(b) If the old chip cost $15 per chip, what will the cost be of the new chip, taking into account the new
area and yield?
9. The following table presents the power consumption of several computer system components. In this
exercise, we will explore how the hard drive affects power consumption for the system.
Component type
Processor
DRAM
Hard drive
Product
Sun Niagara 8-core
Performance Power
1.2 GHz
72-79W peak
Intel Pentium 4
Kingston X64C3AD2 1 GB
Kingston D2N3 1 GB
DiamondMax 16
DiamondMax Plus 9
2 GHz
184 pin
240 pin
5400 rpm
7200 rpm
48.9-66W
3.7W
2.3W
7.0W read/seek, 2.9W idle
7.9W read/seek, 4.0W idle
(a) Assuming the maximum load for each component, and a power supply efficiency of 75%, what
wattage must the server’s power supply deliver to a system with an Sun Niagara 8-core, 4 GB 240 pin
Kingston DRAM, and one 7200 rpm hard drive?
(b) How much power will the 7200 rpm disk drive consume if it is idle roughly 40% of the time?
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(c) Given that the time to read data off a 7200 rpm disk drive will be roughly 75% of a 5400 rpm disk, at
what idle time of the 7200 rpm disk will the power consumption be equal, on average, for the two disks?
10. Imagine that your company is trying to decide between a single-processor system and a dualprocessor system. Table below gives the performance on two sets of benchmarks: a memory benchmark
and a processor benchmark. You know that your application will spend 20% of its time on memorycentric computations, and 75% of its time on processor-centric computations.
Chip
# of cores
Athlon 64 X2
Pentium 4
2
1
Clock
Frequency(MHz)
3,200
2,800
Memory
Performance
2,940
2,730
Dhrystone
Performance
17,100
7,600
(a) Calculate the weighted performance of the benchmarks for the Pentium 4 and Athlon 64 X2.
(b) How much speedup do you anticipate getting if you move from using a Pentium 4 to an Athlon 64 X2
on a memory-intensive application suite?
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