Title page for ETD etd-09122011-125316

Type of Document Master's Thesis
Author Saha, Sonal
Author's Email Address sonal3@vt.edu
URN etd-09122011-125316
Title An Experimental Evaluation of Real-Time DVFS Scheduling Algorithms
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Ravindran, Binoy Committee Chair
Broadwater, Robert P. Committee Member
Plassmann, Paul E. Committee Member
  • Dynamic Voltage and Frequency Scaling
  • Real-Time Linux
Date of Defense 2011-09-09
Availability unrestricted
Dynamic voltage and frequency scaling (DVFS) is an extensively studied energy manage-

ment technique, which aims to reduce the energy consumption of computing platforms by

dynamically scaling the CPU frequency. Real-Time DVFS (RT-DVFS) is a branch of DVFS,

which reduces CPU energy consumption through DVFS, while at the same time ensures that

task time constraints are satisfied by constructing appropriate real-time task schedules. The

literature presents numerous RT-DVFS scheduling algorithms, which employ different tech-

niques to utilize the CPU idle time to scale the frequency. Many of these algorithms have

been experimentally studied through simulations, but have not been implemented on real

hardware platforms. Though simulation-based experimental studies can provide a first-order

understanding, implementation-based studies can reveal actual timeliness and energy con-

sumption behaviours. This is particularly important, when it is difficult to devise accurate

simulation models of hardware, which is increasingly the case with modern systems.

In this thesis, we study the timeliness and energy consumption behaviours of fourteen state-

of-the-art RT-DVFS schedulers by implementing and evaluating them on two hardware plat-

forms. The schedulers include CC-EDF, LA-EDF, REUA, DRA andd AGR1 among others,

and the hardware platforms include ASUS laptop with the Intel I5 processor and a mother-

board with the AMD Zacate processor. We implemented these schedulers in the ChronOS

real-time Linux kernel and measured their actual timeliness and energy behaviours under

a range of workloads including CPU-intensive, memory-intensive, mutual exclusion lock-

intensive, and processor-underloaded and overloaded workloads.

Our studies reveal that measuring the CPU power consumption as the cube of CPU fre-

quency can lead to incorrect conclusions. In particular, it ignores the idle state CPU power

consumption, which is orders of magnitude smaller than the active power consumption.

Consequently, power savings obtained by exclusively optimizing active power consumption

(i.e., RT-DVFS) may be offset by completing tasks sooner by running them at the highest

frequency and transitioning to the idle state earlier (i.e., no DVFS). Thus, the active power

consumption savings of the RT-DVFS techniques’ that we report are orders of magnitude

smaller than their simulation-based savings reported in the literature.

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