Presentation by Antonio Paolillo (HIPPEROS) at the 24th ACM International Conference on Real-Time Networks and Systems (21st October 2016)

1. Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System
Antonio Paolillo - Ph.D student & software engineer
24th ACM International Conference on Real-Time Networks and Systems
21th October 2016

2. 2

3. Goal:
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4. Goal:
Parallelism helps to reduce energy
while meeting real-time requirements
4

5. 5
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

6. 6
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

7. 7
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

8. 8
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

9. 9
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

10. 10
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

11. 11
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

12. 12
Quantifying Energy Consumption
for Practical Fork-Join Parallelism
on an Embedded Real-Time Operating System

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55. Combine:
● parallel task model
● Power-aware multi-core scheduling
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Save more with parallelism? Yes!

56. Combine:
● parallel task model
● Power-aware multi-core scheduling
→ validated in theory → malleable jobs (RTCSA’14)
56
Save more with parallelism? Yes!

57. This work
Goal:
Reduce energy consumption as much possible
while meeting real-time requirements.
57

58. This work
Goal:
Reduce energy consumption as much possible
while meeting real-time requirements.
Validate it in practice
58

59. Validate in practice
● Parallel programming model
● RTOS techniques → power-aware multi-core hard real-time scheduling
● Evaluated with full experimental stack (RTOS + hardware in the loop)
● Simple, but real application use cases
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60. 1. Run-time framework
2. Task model and analysis
3. Experiments
60

61. 1. Run-time framework
2. Task model and analysis
3. Experiments
61

62. Run-time framework
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MPSoC platform

63. Run-time framework
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MPSoC platform
RTOS
& lib support

64. Run-time framework
64
MPSoC platform
RTOS
& lib support

65. Run-time framework
65
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark

66. Run-time framework
66
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark

67. Parallel programming model
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68. (Simple) Parallel Program
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69. (Simple) Parallel Program Flow
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70. (Simple) Parallel Program Flow
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71. An embedded RTOS
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72. An embedded RTOS
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● Micro-kernel based
● Natively supports multi-core
● Provides hard-real time scheduling
● Power management fixed at task level
We developed HOMPRTL
→ OpenMP run-time support for HIPPEROS.

73. 1. Run-time framework
2. Task model and analysis
3. Experiments
73

74. Parallel task model
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75. Parallel task model
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76. ● Sporadic fork-join
● Arbitrary deadlines
● Rate monotonic based analysis
● Threads are partitioned
● 3 stages, very simple
Parallel task model
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77. ● Symmetric Multi-Core
● Global DVFS, finite set of operating points 〈 Vdd
, f 〉
● Power increases monotonically with frequency
Platform model
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78. Optimisation & partitioning process
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Power optimisation
Partitioner
Schedulability test

79. Optimisation & partitioning process
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Power optimisation
Partitioner
Schedulability test
Axer et al
proved wrong (shepherding)

80. 1. Run-time framework
2. Task model and analysis
3. Experiments
80

81. 1. Run-time framework
2. Task model and analysis
3. Experiments
a. Testbed description
b. Single use cases
c. Task systems
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82. 1. Run-time framework
2. Task model and analysis
3. Experiments
a. Testbed description
b. Single use cases
c. Task systems
82

83. Experimental stack
83
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark

84. Experimental stack
84
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark

85. Experimental stack
85
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark
Measurement
framework

86. Experimental stack
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MPSoC platform
RTOS
& lib support
Parallel app.
benchmark
Measurement
framework

87. Target platform - i.MX6q SabreLite
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● Embedded board ARM Cortex A9 MP
● Supported by HIPPEROS
● 4 cores, but global DVFS
● Operating points

88. Operating points
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89. Operating points
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MPSoC
Embedded board

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MPSoC
Embedded board
Power supply
220 V
220 V
Transformer
5 V

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MPSoC
Oscilloscope
Embedded board
Power supply
220 V
220 V5 V
R
Voltage
measurements
P = V² / R
Transformer

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MPSoC
Control Computer
Oscilloscope
Embedded board
Power supply
220 V
220 V5 V
R
Serial
JTAG
USB
Captured data
transfer
Oscilloscope
trigger
Voltage
measurements
P = V² / R
Transformer
HIPPEROS
Inputs Outputs
Serial

94. Use cases
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MPSoC platform
RTOS
& lib support
Parallel app.
benchmark
Measurement
framework

95. Use cases
95
MPSoC platform
RTOS
& lib support
Parallel app.
benchmark
Measurement
framework
π
AES
Image

96. ● Different workloads
● Easy OpenMP implementation
● Good scaling expected
Use cases
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Image
AES π

97. 1. Run-time framework
2. Task model and analysis
3. Experiments
a. Testbed description
b. Single use cases
c. Task systems
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98. Use case alone - voltage probe output
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99. Use case alone - converted to power values
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100. Use case alone - execution time measurement
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101. Use case alone - peak power measurement
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102. Use case alone - energy measurement
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103. Use case alone - execution time
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104. Use case alone - peak power
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105. Single core power consumption
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P ∝ Vdd
2
f
Vdd
∝ f

106. Single core power consumption
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P ∝ Vdd
2
f
Vdd
∝ f
→ P ∝ f3

107. Multi-core power consumption
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P ∝ k f3

108. Use case alone - peak power
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P ∝ k f 3

109. Use case alone - energy
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110. Execution time speedup
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Frequency scaling OpenMP parallelism

111. 1. Run-time framework
2. Task model and analysis
3. Experiments
a. Testbed description
b. Single use cases
c. Task systems
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112. System experiments
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113. ● Generate 232 random task systems (U = 0.6 → 2.9)
System experiments
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114. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
System experiments
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115. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
● Scheduling test & optimisation in Python for 1, 2, 3, 4 threads
System experiments
115

116. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
● Scheduling test & optimisation in Python for 1, 2, 3, 4 threads
● Operating points and threads partition for each task
System experiments
116

117. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
● Scheduling test & optimisation in Python for 1, 2, 3, 4 threads
● Operating points and threads partition for each task
● Generate HIPPEROS builds
System experiments
117

118. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
● Scheduling test & optimisation in Python for 1, 2, 3, 4 threads
● Operating points and threads partition for each task
● Generate HIPPEROS builds
● Run feasible systems and measures
System experiments
118

119. ● Generate 232 random task systems (U = 0.6 → 2.9)
● Bind generated tasks to use cases
● Scheduling test & optimisation in Python for 1, 2, 3, 4 threads
● Operating points and threads partition for each task
● Generate HIPPEROS builds
● Run feasible systems and measures
System experiments
119

120. Energy consumption
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121. Relative energy savings
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122. Conclusions
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● Practical experimental framework flow for parallel real-time applications
● Parallelisation saves up to 25% energy (the whole board)
● Confronted theory with practice
○ Speedup factors
○ Power measurements
● Challenge: integrate “OpenMP-like” programs in industry systems

123. Conclusion
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Parallelism helps to reduce energy
while meeting real-time requirements

124. Thank you.
124

125. Questions?
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126. Dynamic power vs static leakage
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P ∝ k f3
+ α k

127. P ∝ k f3
+ α k
Dynamic power vs static leakage
127
dynamic static

128. Dynamic power vs static leakage
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dynamic static
● α is platform-dependent
● Comparison between DVFS and DPM
P ∝ k f3
+ α k

129. ● 232 systems for each degree of //
○ No high utilisation systems
→ Partitioned Rate Monotonic
○ Only feasible systems for 1 → 4 threads
● More threads consume less
● Low utilisation systems don’t need
high operating points (often idle)
● Analysis is pessimistic
for high number of threads
Energy consumption
129

130. ● Same systems, but rel. to 1 thread
● Parallelism helps to save energy :-)
● < 0.13, but not a lot of systems...
● “4 threads” dominates
● ↗ Utot
⇒ ↘ energy
○ Until Utot
= 2.4
○ For high Utot
:
■ Analysis pessimism
■ Schedulable systems only bias,
so already well distributed
■ Some systems are only schedulable in parallel
Relative energy savings
130

131. ● “3 threads” is bad:
○ Loss of symmetry with 4 cores
○ Different tasks executes simultaneously (1+3)
● Measures on the whole platform
○ CPU alone would give better results
● Need more data
○ Charts would be smoother
○ But it takes time…
■ 1 minute/execution
■ 4 executions/system
■ 232 systems, ≈ 15 hours
Questions on experiment results
131

132. ● Flawed, but does not impact results
○ Axer et al (ECRTS’13)
○ Flaw pointed by Fonseca et al (SIES’16)
● Scheduling framework
○ Part of the technical framework
○ Not the important contribution/result
● Will be improved with future work
Analysis technique
132