2.3 Energy Efficient Workflow Scheduling
2.3.2 Energy-efficient scheduling of workflows
Now we present a few seminal works where minimization of energy consumption is considered as the main or one of the co-objectives. For instance, Pietri et al.
[101] proposed two energy-efficient algorithms for executing a set of workflows on a virtualized cloud environment where they aimed at reducing energy consumption while maintaining the cost budget and deadline constraint.
Durilloet al. [102] has developed a multi-objective energy-efficient list-based work- flow scheduling algorithm, called MOHEFT (Multi-Objective HEFT) where they
present a trade-off between the energy consumption and the makespan time. They performed extensive experiments with different workflow characteristics. The pro- posed algorithm achieved shorter or same makespan time as compared to HEFT algorithm but with lesser energy consumption. Cao et al. [103] proposed energy- efficient scheduling technique for executing a set of scientific workflows in a col- lection of data centers. Depending on the amount of energy consumption, they considered four different modes for servers: active, idle, sleep and transition in their work. Authors used the DVFS technique and tasks were run at optimal frequencies to reduce the energy consumption. In [28], Bousselmi et al. initially partitioned the workflow to reduce network energy consumption by reducing the amount of data communication among them. Then in the next step, they used the cat swarm optimization based heuristic to schedule each partition on a set of VMs in an energy-efficient manner. Chen et al. [104] designed an online scheduling algorithm, called, energy-efficient online scheduling,EONS to schedule tasks from different workflows. System resources are dynamically adjusted to maintain the weighted square frequencies of the hosts.
Recently, Liet al. [61] addressed both energy consumption and the execution cost while guaranteeing the deadline constraints of the tasks. The authors considered an hourly based pricing model for the VMs and a task is mapped to an optimal VM. They developed strategies to merge sequence tasks and parallel tasks for meeting performance constraints by reducing execution cost and energy consump- tion. They have also used the DVFS technique to use the slack time efficiently.
Xu et al. [41] considered the execution of online scientific workflows to minimize the energy consumption of cloud resources. The authors transformed the workflow into a set of sequential tasks. They applied a static time partitioning to calculate the arrival time of the individual task of the workflow. The authors considered homogeneous VMs with heterogeneous hosts. At the time of scheduling, the sched- uler considers all the running tasks as new tasks with possibly lesser length and schedules them along with the current tasks. We consider a similar setup in our last contribution where we deal with scheduling real-time dependent tasks.
Table 2.1 lists some seminal work in the area of energy-efficient scheduling policies for the cloud environment. The table also contains the key considerations of each of the work and some lacunae in their work.
Research work Key considerations Major lacunae Hotta et al. [70] DFVS; Split program
execution
Manual program instrumentation Calheiros and Buyya
[73]
DVFS; Four different
operating conditions Only one VM per core Zhu et al. [30] Rolling horizon
optimization
Considers only dynamic energy; host utilization
100%
Wu et al. [52]
Minimum and maximum frequency for tasks and
servers
No proper construct for energy consumption;
Number of VMs in a host determines the SLA Lee and Zomaya in [45] Maximizes resource
utilization to save energy
No task order; Schedules immediately as a task
arrives Xiao et al. [86] Threshold on utilization;
load prediction
No justification on Threshold values;
Difficult if application dependent
Farahnakian et al. [94]
Bi-directional bin packing using CPU and
memory
Migration cost is calculated based on VM
memory only; No clear mapping for tasks to
VM
Ye et al. [88]
Co-location effect of different types of workloads; Migration
count
Studied only four types of applications;
Performance depends on target conslidation
scenario Mastroianni et al. [85]
VM consolidation considering CPU and
RAM
Only VM to host allocation; No task
characteristics Cao et al. [103] DVFS with four different
modes for servers
Do not consider the deadline constraints of
the tasks or workflow Pietri et al. [101]
Two approaches for scientific workflow:
budget-constrained and deadline-constrained
Homogeneous hosts;
Migration is not considered Bousselmi et al. [28] Network energy
consumption
No deadline is considered; Not suitable
for online data Xu et al. [41] Homogeneous VMs on
heterogeneous hosts
Static partitioning of tasks; Migration not
considered Table 2.1: Some major works in the area of energy-efficient scheduling in cloud
computing environment
Scheduling Online Real-Time Tasks on LMTMPS
This chapter first presents an energy-efficient scheduling policy for executing a set of online independent real-time tasks on a large computing system where the processors are empowered with the multi-threaded facility. We term this kind of computing systems as Large Multi-threaded Multiprocessor Systems (LMTMPS).
Further, the chapter presents three variations of the basic scheduling policy to efficiently handle some special cases. The proposed scheduling policies consider a thread-based power consumption model which is devised based on the power consumption pattern of some of the recent commercial processors.
3.1 Introduction
Nowadays, various scientific and real-time applications of different domains such as avionics, bioinformatics, signal processing, image processing, etc. are being deployed in the large systems, for their efficient execution [24, 27]. These ap- plications typically consist of hundreds of compute-intensive, data-intensive and communication intensive tasks. Thus a significant amount of resource is required to execute these applications. On the other hand, the compute systems of today’s world is equipped with a large number of processors and these processors are em- powered with the multi-threaded feature. Thus the processing capability of these systems is sufficient enough to handle these high-end applications. But with an increase in the processing capability, the energy consumption of these large sys- tems is also increasing. This growing energy consumption has sought the attention
0 50 100 150 200 250
0 1 2 3 4 5 6 7 8 9
Power consumption (in Watts)
Number of active threads
Phenom II X6 Intel i7-860 Qualcom HexaV3 Phenom 9900 Core 2 Quad Q9450 Core 2 Quad Q6600
Figure 3.1: Power consumption plot of a few recent commercial processors with number of active threads [2, 3]
Power Consumption (in Watts)
#Active-threads→ 1 2 3 4 5 6 8 Processor ↓
Phenom-II-X6 40 58 73 88 103 115 - Intel i7-860 165 174 186 193 204 212 228 Qualcom Hexa V3 40 55 60 72 82 90 - AMD-Phenom-9900 76 95 114 131 - - - Core-2-Quad Q9450 28 41 53 58 - - - Core-2-Quad Q6600 48 62 72 79 - - - Table 3.1: Power consumption behaviour of commercial processors [2, 3]
of the research community of to a great extent. As a result, a good number of scheduling algorithms for reducing the energy consumption of such large systems are proposed [53, 76, 50, 70, 71, 55]. Majority of these research consider power consumption at a finer granularity and use the DFVS technique to reduce the en- ergy consumption. For instance, Hottaet al. [70] split the program execution into multiple regions and each region is executed using an optimal frequency for that region. Ge et al. [50] considered a distributed DVFS environment to reduce the energy consumption of the cluster. But none of these energy-efficient scheduling approaches for the large systems sufficiently consider scheduling of the real-time tasks in their work. In this chapter, we consider scheduling of online real-time tasks for a large multi-threaded multiprocessor system and consider the power construct at a coarser granularity.
Figure 3.1 shows a plot of the power consumption of a few recent multiproces- sors (multi-threaded processors) versus the number of running hardware threads (HTs) in them. We see that the power consumption values follow an interesting
pattern. Whenever a processor gets switched on and executes a task using one HT (processor with one active thread), it consumes a significant amount of power.
After that addition of subsequent active thread, the additional power consump- tion of processor due to the additional thread is small. So power consumption of already switched on processor due to the addition of an active thread is incre- mental. For example, Qualcom Hexa V3 consumes 40 watts with 1 active thread (power consumption values are also listed in Table 3.1). When it runs its 2nd thread, it consumes 55 watts. The difference 15 watts (= 55−40) is the power consumption for the 2ndthread. Similarly, on activation of subsequent threads, the processor consumes additional 5 watts (= 60−55), 12 watts (= 72−60), 10 watts (= 82−72) and 8 watts (= 90−82) respectively. A similar power consumption pattern is observed in case of Intel Xeon Gold processors [105]. For instance, for a given workload, Xeon Gold 6138 processor with 20 cores consumes 60 watt when it starts execution with 1 core. Then the power consumption increases linearly with active core count until it reaches 107 watt for 10 cores. Further, the power consumption increases and reaches 127 for active core count of 20. Following this interesting power consumption characteristics of a few commercial multiprocessors (multi-threaded processors), we devise a simple but elegant power consumption model both for the single processor and for the whole compute system. The exist- ing scheduling algorithms for the real-time tasks do not consider this interesting power consumption behavior of the processors.
The contributions of this chapter can be summarized as follows.
• We derive a simple but elegant power consumption model for the proces- sors following the power consumption characteristics of some of the recent multiprocessors (multi-threaded processors) and used this model to measure the processor power consumption while scheduling a set of online real-time tasks.
• We propose four energy-efficient real-time scheduling policies, named (a) smart scheduling policy, (b) smart - early dispatch scheduling policy, (c) smart - reserve scheduling policy and (d) smart - handling immediate ur- gency scheduling policy to reduce the total energy consumption of the system without missing deadline of any task.
• As the execution time and deadline of tasks play a significant role in schedul- ing, we consider six different execution time schemes and five different dead- line schemes for the tasks in our work.
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Figure 3.2: Online scheduling of real-time tasks on LMTMPS
• We examine the instantaneous power consumption for different scheduling policies and then compare the overall energy consumption of our proposed policies with five different baseline scheduling policies for both real-world trace data and synthetic data covering a wide range of variations.