=Paper=
{{Paper
|id=Vol-2145/p06
|storemode=property
|title=Optimal Workflow Scheduling In Cloud Computing Using AHP Based Multi Objective Black Hole Algorithm
|pdfUrl=https://ceur-ws.org/Vol-2145/p06.pdf
|volume=Vol-2145
|authors=Fatemeh Ebadifard,Seyed Morteza Babamir
}}
==Optimal Workflow Scheduling In Cloud Computing Using AHP Based Multi Objective Black Hole Algorithm==
Optimal Workflow Scheduling In Cloud Computing Using AHP Based Multi Objective Black Hole Algorithm Fatemeh Ebadifard Seyed Morteza Babamir Department of Computer, Depertment of Computer University of Kashan, Kashan, Iran University of kashan, Kashan, Iran Ebadifard.fatemeh@gmail.com Babamir@kashanu.ac.ir Abstract— Cloud computing is one of the fields that has attracted in light of these objectives [2]. This problem is presented as a lot of attention in recent years. Task scheduling meaning the multi-objective scheduling, and there are different approaches to proper permutation of user requests on virtual machines is one of solve it. One of these methods is the use of Pareto optimal the most important challenges in the cloud environment due to the solutions. This solution allows users to have the best choices increase in virtual machines as well as the diversity of users with from the set of appropriate solution and thus provide a set of different service quality requirements and therefore task ultimate solutions that include optimal tradeoff between some of scheduling is a NP-hard problem. This becomes more complicated the QoS objectives. when quality of service objectives conflict with each other; therefore, service providers for the proper use of cloud In this paper we have expanded our previous work [3] which environment capabilities require an optimal trade-off between the is based on the black hole algorithm [4] and it is a heuristic various objectives and in such cases heuristic algorithms can be optimization method which can be used as an appropriate used for optimal scheduling. To this end, we extended a recent solution to the scheduling problem due to its simple structure heuristic algorithm called Black hole and considered dependency and lack of dependence on external parameters and its high graph of workflow tasks. The proposed method combines the performance. heuristic algorithm and decision-making method (AHP) to solve the multi-objective workflow scheduling problem on virtual The extension is carried out in 2 aspects: (1) making our machines. We converted the single-objective Black-hole algorithm previous work an AHP-based algorithm and using this feature to into a multi-objective by using the AHP relationship, and then it is select the optimal solutions. To this end, we apply combination used to solve the scheduling problem. We have implemented our of multi-objective black hole approach and Decision-Making proposed method using the Workflowsim tool and have compared method (AHP) [5] for workflow scheduling optimization. So, the results with multi-objective algorithms SPEA2 and NSGA2 we have been able to develop the domination relationship in the based on the parameters of Makespan and cost and resource utilization using a balanced and unbalanced workflow. multi-objective algorithm by using AHP method, as a result we could choose better solution according to the preference of users Keywords- Cloud Computing; Workflow; Scheduling; Multi in the Pareto front. objective; Decision-Making method ;AHP. (2) Presenting resource utilization objective to consider provider’s preferences in selection of the best solution among I. INTRODUCTION the optimal solutions. So that the proposed method can consider Workflow is a common model for modeling most scientific the quality of service requirements for service provider and the programs which contains a number of tasks and data client simultaneously. dependencies between tasks. Since most tasks in applications are Our main contributions can be summarized as follows: a set of workflows; in recent years, extensive research has been 1: Presentation of the multi-objective Black hole algorithm using done on the workflow scheduling in the cloud environment. the single-objective Black hole algorithm and Pareto optimizer Workflow scheduling on resources is to select the appropriate and applying it for the multi-objective workflow scheduling in virtual machine for a task, so that its related tasks are already the cloud environment executed. This selection of resources and assignment of task on 2: Using the AHP technique in multi-objective domination them depends on the requirements of quality of service for relationship and taking into account the preferences of users in different users and since there are different permutation of the solution of workflow scheduling requests on virtual machines, task scheduling is a NP-hard 3: Targeted evaluation and analysis to illustrate the effective problem [1]. combination of the black hole algorithm with AHP technique to A great related work has already been done on the workflow reduce Cost of resources and makespan and increase resource scheduling problem in the cloud environment; in most classic utilization. work, it is tried to reduce finish time, but in recent ways; in We have used the WorkflowSim tool [6], which is an addition to Makespan, there are other objectives, such as extension of CloudSim [7] open source tool, to evaluate our resource utilization and cost for scheduling. And they seek to proposed method. We have developed the initial core of this tool provide an optimal permutation of requests on virtual machines, to provide our algorithm and then compared our proposed Copyright held by the author(s). 36 method with previous Pareto-based algorithms such as SPEA2 RDPSO algorithm. Most of the previous methods have only [8], NSGA2 [9]. considered two objectives of cost and makeapn reduction as optimization objectives; Khalili et al. [18], in their proposed The rest of the paper is comprised of the following sections: method, in addition to Makespan and cost, also considered the Section 2 presents the related work of workflow scheduling. In purpose of resource efficiency and using a gray wolf algorithm, Section 3, the mathematical model of the workflow scheduling they have introduced a new Pareto-based multi-objective problem and the details of the optimization objectives used have scheduling method. In our proposed approach, in addition to been provided and in the fourth section, we first introduced the reducing the cost, Makespan that benefits of the users are single-objective black hole algorithm and the AHP technique supplied; increased resource utilization for the benefit of service and then we present the details of the proposed AHP-based providers has been considered. The difference of our work with multi-objective algorithm, in the fifth part, we have described previous methods is to use the new Black Hole heuristic the details of the evaluation of the proposed method and algorithm, which is more efficient than other algorithms and analyzed the results. Finally, in the final section, conclusions and converting it to a multi-objective algorithm is done using the future work have been presented. Pareto optimizer. Also, in the proposed algorithm by combining II. RELATED WORK black hole algorithm with the decision-making method (AHP), the QOS preferences are considered by the user during the Many previous work have been done to solve the problem of execution of the algorithm and this will reduce the search space task scheduling for independent workload and workflow in the of the problem and choose the more optimal solutions with cloud environment; since our proposed approach has been increasing requests and the variety of virtual machines. provided for the workflow, we investigate the methods of workload scheduling. There are different types of classification III. PROBLEM FORMOULATION for workflow scheduling methods; for example, static or A set of tasks and edges for communication between dynamic scheduling or other categorization based on single- requests is defined as workflow and in this workflow child objective or multi-objective workflow scheduling. In this request is not allowed to be execute as long as the parent is not section, we examine the multi-objective workflow scheduling executing. Figure 1 illustrates an example of a workflow in methods. In multi-objective scheduling, several objective which which each node represents a task and edges are the connection are often in contradictory have been considered as optimization between tasks and the number above each edge shows the objectives and provide the optimal tradeoff of solutions. Multi- estimated cost for data transfer between the corresponding tasks. objective scheduling methods are in the following categories: In the following, each of the objectives that we have used in the A. Aggregation approach workflow scheduling problem will be explained. One of the multi-objective scheduling methods is to convert a multi-objective problem to a single objective which is done by 1 t 0 t 0 weighting objectives. In Li et al. [10], have converted the multi- 2 4 1 objective problem into a single objective by using the heuristic method CCSH and have provided a scheduling method with cost 1 3 1 t t t t and Makespan reduction objectives. Dongarra et al. [11] have 7 0 2 5 proposed a scheduling method by using aggregation technique 1 to increase performance and reliability. They have provided 2 2 (RDLS) a reliable dynamic level scheduling algorithm based on t 4 t the DLS algorithm [12]. Dogan et al. [13] have improved their 3 6 method using genetic algorithm and BDLS scheduling method. Figure. 1. The workflow sample B. Pareto based approach Unlike the previous method, in which only one definitive A. Makespan solution is presented as the result of the algorithm. In these To formulate the problem we have denoted a set of tasks methods, a set of non-dominated solutions is provided that Task = {t1, t2, ..., tn} where i {1, 2,..., n} . We have defined a allows users to choose a solution based on their expected QoS. set of m virtual machines, VM = {VM1, VM2, ...., VMj} Yu et al. [14] have used multi-objective evolutionary algorithms interconnected by network where j {1, 2,..., m} . The tasks will (MOEAs) to solve the workflow scheduling problem. This approach is aimed at reducing two conflicting objectives of cost be processed on virtual machines. Completion time of task Ti on and runtime. In addition to these two purposes, they also virtual machine VMj are denoted as CTij respectively. Overall considered deadline and budget constraints in the algorithm and task completion time is called makespan and is defined by Eq. therefore provided fitness functions corresponding to objectives (3-1) and constraints. The population-based algorithms SPEA2 and n Makespan max CTti xij VM j NSGAII [8, 9] and local search-based algorithms MOEA, PAES (3-1) [15] have been provided for workflow scheduling based on 1 j m i 1 different objectives and constraints. Various scheduling If the request ti is running on VMj, value of xij is equal to 1 methods have been proposed for cost and Makespan reduction otherwise is zero. Figure. 2 epitomizes a sample scheduling using heuristic algorithms and Pareto optimization; such as makespan for 6 tasks and 3 VMs. Udomkasemsub et al. [16] using ABC and WU [17] using the 37 C. Resource utilization: For each virtual machine, resource utilization was defined Makespan as the Eq.3-8. Where xij is equal to 1, if the request ti is executing on VMj otherwise is zero. VM Task1 Task4 n 1 (3-8) Utilization PT ij VM Task2 Task6 VM j i 1 2 Makespan VM Task3 Task5 3 IV. PROPOSED METHOD Figure. 2. Completion time of a typical workflow Heuristic algorithms have been used effectively in most optimization issues. Among them, the Black Hole heuristic B. Cost algorithms can provide more optimal solutions for workflow In cloud computing, computational cost for each customer is scheduling problem in terms of its appropriate structure and calculated based on the timespan they use of resource at any efficiency compared to the PSO and GA algorithms. In this time. Total cost for each request include: section, we have first introduced the standard black hole algorithm and then, after expressing the AHP technique, we B.1. Computational cost: present the details of the AHP-based multi-objective black hole This cost is calculated based on execution time of the request algorithm. ti on the VMj and cost per processing in VMj by Eq.3-2 and the A. Standard Black Hole Algorithm execution time of the request ti is calculated by Eq.3-3. The black hole algorithm is a population-based heuristic (3-2) C p (ti ) ETtiVMj Cos tPer Pr occes sin ginVmj algorithm which was first presented by Mr. Hamtlou In the first step, this algorithm generates an initial population from (3-3) ET VM MI (ti ) ti j candidate solutions (stars) randomly in a sample space. In the MIPS (VM j ) workflow scheduling problem on virtual machines, each While MI (ti) is the number of instructions of request i and solution is a permutation of requests on virtual machines. The MIPS (VMJ) is the number of million instructions that the value of the fitness function is calculated for each star and the machine j executes per second. star with the best value for the objective function is selected as B.2. Cost per storage: Black Hole. The black hole is capable of absorbing the stars that have trapped it. After the black hole absorbs the stars around it, This cost is calculated based on the time that this task is the remaining stars move toward the black hole. The motion of placed on the virtual machine and it is calculated according to the stars towards the black hole is based on Eq. (4-1). Eq.3-4. (4-1) xi (t 1) xi (t ) rand ( xBH xi (t )) i 1, 2,..., N (3-4) Cs (ti ) ( ETtiVMj WTtVMj ) Cos tPerStoragInVMj i Where 𝑥𝑖 is the position of the star i at time t and t + 1. xBH is the position of the black hole in the search space and rand is a WTtiVMj has been the waiting time of request ti on the virtual random number in the range [0,1] and N is the number of stars machine VMj which has depended on the time for providing (candidate solutions). required files from its parent and is calculated according to Eq. This evolution of solutions continues until the algorithm 3-5. termination condition is reached and at any stage, if a star has a better fitness function than a black hole, then that star replaces (3-5) WT VMj max input (ti ) the black hole. The black hole algorithm can prevent being ti BW trapped in the local optimal due to the elimination of the B.3. Cost per transfer: available stars in the range of the best solution and selection the This costs is dependent on the cost that request ti should pay alternate star randomly in search space. The radius of the for the transfer of files to their children which is calculated horizons in the black hole algorithm is calculated using Eq. (4- according to Eq. 3-6. 2). (4-2) R f BH Output (ti ) n (3-6) C (t ) T i BW Cos tPerTransfer f i 1 i The total cost is calculated by Eq. 3-7. Cloud provider Where fBH is the fitness of black holes and fi is the fitness calculates the cost of request ti based on the total cost presented function of the star i and n is the number of stars. When the below. distance between a star and a black hole is less than R, that star (3-7) Ctotal (ti ) C p (ti ) Cs (ti ) CT (ti ) is eliminated and a new star is created randomly in search space. 38 B. AHP decision making method And m is equal to the number of objectives that in this case AHP is a multi-criteria decision-making approach which can study is equal to the number of the optimization objectives be used to solve complex decision problems; it was presented by means 3. Saaty [5] that has been established based on using a set of To calculate priority, we use the concepts of Normalization pairwise comparisons. The main steps of Analytic Hierarchy and weighted average. As first the geometric mean of each row Process (AHP) includes making a hierarchy, Assign weight to has been calculated and then we do normalization. The values each metric, investigate the Consistency check of system and obtained from calculations that make up the priority column are ultimately decision-making (determine the priorities of options) called eigenvector (λ). Similarly, we perform priority determination for Pareto optimal set for each criterion. B.1: Making hierarchy: In the first step, the decision-making elements and the B.3: Consistency check: relationships between them must be known in order to build Consistency check is one of the advantages of AHP which hierarchy. So the options that have an impact on decision making aims to testing coordination of the important degree between are at the lowest level Thus objectives that have an impact on each metric. The concept of consistency can be expressed as if decision making are considered at lower ranks and decision objective A is more important compared to B and objective B making whole objective is considered at top of the hierarchy, is more important compared to the C, the consistency check is and finally decision-making options are placed in the lowest established if the A is more important than C . The consistency level. In following an example for workflow scheduling problem index (CI) is shown by Equation (4-3) which QoS criteria includes Makespan, cost and resource max m utilization, the hierarchy structure is shown in Figure. 3. In this (4-3) CI m 1 example Studied options are members of the Pareto front, which indeed one of them should be selected. And consistency ratio is calculated by Equation (4-4) (4-4) CR CI RI Purpose Optimal workflow In Equation (4-4) RI value is obtained from the random scheduling consistency index table. If value of CR is CR<0.1 consistency is acceptable otherwise contents of Matrix A should be revised. B.4. Decision making and selecting definitive solution: Objective Make Cost Resource The final step of analytic hierarchy process includes span Utilization determining the importance of each decision-making option in relation to the criteria and general purpose of desired problem. The final weight of each option is calculated of sum of multiplying the priority of objective in weight of options in Pareto optimal Set S1 S2 … S10 accordance with the Equation (4-5) m (4-5) Pi Wi Gi i 1 Figure. 3. The AHP hierarchy model That Gi is weight of options and Wi is weight of the objective. In this study we have considered the same weight for B.2: Weight calculation: options that those options are Pareto front in workflow Objectives are compared with each other pairwise to scheduling problem. Members who value of Pi are less than determine the relative priority of each metric (weight), this other options are more appropriate than the rest of the members. Pairwise Comparison construct pairwise comparison matrix A. It should be noted, the inverter form of resource utilization has For example, comparing the importance between the Makespan been used because Makespan and cost should be minimized and of workflow and its cost indicates that which one has the higher resource utilization should be maximize in the optimization of degree of impact in finding the optimal solution. Numbers 1 to the scheduling problem. 9 are usually used to pairwise comparison. 1 means the same C. AHP base multi objective black hole importance and 9 shows the highest degree of importance. Pairwise comparison matrix is shown with 𝐴 = (𝑎𝑖𝑗 )𝑚×𝑚 and is Pareto optimal set in heuristic multi-objective algorithms often involves non-dominated solutions and an optimal tradeoff as follows: between objectives. Users decide between the optimal solutions, a11 a12 a13 based on their preferences between objectives and choose the A a21 a23 right solution which includes permutations of requests on virtual a22 machines. In such cases, in order to choose the right solution a31 a32 a33 among the Pareto optimal set, we need to have a precise weight of the objectives corresponding to user preferences. Without the 1 precise weight of the objectives, choosing the solution Where aii=1 and aij= proportional with the user's preferences is difficult. That's why a ji 39 users after finding out the set of non-dominated solutions, use circumstances, one can consider each as the optimal decision. AHP-like techniques to choose the optimal solution that suits the Algorithm 1 depicts the pseudocode of the AHP Base Multi user's preferences. We have also used the AHP technique in our objective Black hole algorithm. proposed method. The difference in our approach with previous works is that we combine the AHP technique with heuristic Algorithm1: AHP base multi objective black hole algorithm pseudo algorithm but in the previous methods [19], after finding Pareto code optimal set in the heuristic algorithm the AHP technique is used. With increasing requests and the diversity of virtual machines, 1. Create an initial population of star randomly and an empty archive the space of the problem increases and the number of solutions 2. While (t< Max number of iterations) 3. Calculate the fitness function for all stars based on Eq.3-1, 3-7, 3-8 in Pareto optimal set increases. As a result, the AHP technique 4. Calculate Pareto based fitness function according to Eq.4-6 may not be able to differentiate between solutions [20]. 5. Calculate final weight of each star by using the AHP technique. In this paper, we combine the AHP technique with the Black 6. Copy top ten non-dominated stars in population to the archive which has Hole heuristic algorithm and, as a result, a new domination the smallest R value and the highest AHP weight value 7. Select the star with the best Pareto base fitness function from the archive relationship has been proposed that, in the proposed domination (Black hole) relationship, the fitness value of a solution, in addition to the 8. For each star solution strong in dominating other solutions, is selected based 9. Update the position of current star according to Eq.4-1 on the amount of final weight of that solution obtained by the 10. Calculate fitness of Pareto according to Eq. 4-6 AHP technique. The details of the proposed algorithm are 11. Calculate the distance between each star and the black hole according to the 4-2 described in detail: 12. If(R< distance) 13. Remove star and create a random star in search space We have used the Pareto-optimization method to convert the 14. End while BH algorithm to PBH algorithm and accordingly, for each star, we have considered two fitness values of R, S. As for each star, based on the number of stars in the archives and the population V. RESULT EVALUATION that this star is dominate, the power of S is calculated. Then, in the next step, we obtain the value of R for each star with respect To evaluate the proposed methods we have used Open to Eq. (4-6). If a star exceeds the upper time boundary and the source, WorkflowSim tools, then we have compared our upper boundary of the cost, then the power of R is given a very simulation results of the proposed method with known radiation- large number. optimizer-based algorithms SPEA2 [8] and NSGA2 [9]. n For evaluation the proposed method we have used a real (4-6) R(i ) (S ) j 1 j workflow library presented by Bahraini et al. [21]. We have used j p a balanced (Ligo) and unbalanced workload (Montage) to j i evaluate the proposed method. Figure.4 shows a small sample of In the above relation, j>i is the symbol of the Pareto these two workflows. domination and j dominate i. In fact, fitness R for a member is determined by the power of its dominators in both the population and archive and the lower R value for each star in Eq. (4-6), the greater fitness of the star because that star is dominated by stars that have less power. In the next step the final weight of each star obtained according to the user's objectives and preferences for each objective, which is achieved using the AHP technique. Then the members of the archives and population set are arranged in ascending order based on its R value and stars with the same R value are arranged by AHP weight and star with larger AHP weight is selected. Therefore The members of population and archive sets are primarily arranged based on R, and secondly, based on AHP (a) (b) weight. The star that has the lowest R amongst all stars in the Figure. 4. The structure of two realistic scientific workflows[22].(a: Ligo) and population and archives is considered as the Black Hole star and (b:Montage) then the position of the stars in the initial population is updated according to the position of the black hole. In the next step, equal We have used a data center consists of twenty hosts and 60 to the number of members in the archive, members are selected virtual machine. Host specification are according to Table 1 and from the top of the arranged list and transferred to the archive characteristics of virtual machine are presented in Table 2. The set. This cycle of procedures is repeated until the achievement input parameters for algorithms PBHO, NSGA2 and SPEA2 are of finish conditions. Non-dominated solutions obtained from also given in Table 3. solving the multi-objective optimization problem (archives) are We repeated our experiments ten times and then reported the often referred to as Pareto fronts. None of the Pareto front average data for three factors Makespan, Cost, and resource solutions are superior to the other and depending on the 40 utilization for two workloads of montage and Ligo in sizes small, medium and large. We have used the decision-making method TABLE 4.A: RESULT OF PBHO, NSGA2 AND SPEA2 FOR MONTAGE WORKFLOW AHP to weigh the objectives that are used in the proposed multi- objective algorithm. If the importance of each objective to be Type Algorithm Makespan Cost Resource considered as following, then matrix A will be as follows: (ms) $ Utilization% Spea2 125.21 4082 0.13 The importance of Makespan in comparison with resource Small utilization: 5, Nsga2 125.49 4083 0.13 PBHO 123.22 4053 0.13 The importance of Cost in comparison with Makespan: 3, Spea2 The importance of Cost in comparison with resource utilization: 270.54 22033 0.32 medium Nsga2 8. 271.84 22299 0.30 PBHO 1 257.11 21720 0.34 1 5 Makespan 3 Spea2 446.1598 45557.59 0.371931 Large A Cos t 3 1 8 Nsga2 485.6466 44624.8 0.347917 THroughput 1 1 PBHO 386.136573 42826.28 0.4073 1 5 8 TABLE 1 HOSTS' TECHNICAL SPECIFICATIONS TABLE4.B: RESULT OF PBHO, NSGA2 AND SPEA2 FOR LIGO WORKFLOW Number of Processing Type Algorithm Makespan Cost Resource Host Ram Hard Bandwidth (ms) $ Utilization% processing speed ID (MB) (MB) (Mbps) Cores (MIPS) Spea2 3130.951 74027.23 0.103792 Small Nsga2 3099.543 74984.73 0.105654 1-20 8 2000000 2048000000 1000000 10000 PBHO 3094.21 72082.71 0.103498 Spea2 3480.52 431702.2 0.464593 TABLE 2 VIRTUAL MACHINE' TECHNICAL SPECIFICATIONS medium Nsga2 3471.826 428138.6 0.479319 Number of Processing Host Ram Hard Bandwidth PBHO processing speed 3322.062 418645.5 0.473009 ID (MB) (MB) (Mbps) Spea2 Cores (MIPS) 3468.511 919475.9 0.960096 Large Nsga2 3478.975 925266.1 0.993529 1-15 1 1000 512 10000 1000 PBHO 3298.811 903725.8 0.968106 16-30 1 1000 512 10000 1000 31-45 2 1000 1024 20000 2000 As it is clear from the results in Table 4-a and 4-b, the amount of cost in all the workloads in all sizes in AHP base multi 46-60 4 2000 1024 20000 2000 objective black hole algorithm is more than other algorithms. Considering that the importance of cost for the user is more than TABLE 3- THE ALGORITHM PARAMETERS other objectives, the proposed method chooses solutions with Parameter Value the lowest cost. Population Size (PBHO, 50 NSGA2,SPEA2) Archive Size 10 (PBHO ,NSGA2,SPEA2) Maximum Iteration 20 (PBHO ,NSGA2,SPEA2) Maximum Generation (SPEA2, 100 NSGA2) Mutation Probability 0.5 (SPEA2, NSGA2) Crossover Probability 0.9 (SPEA2, NSGA2) Weight of Objectives is obtained as w = (0.2718, 0.6612, 0.0670) and the value of CR = 0.04 <0.1, and therefore compatibility is acceptable. Table 4 shows the values of the Makespan, resource utilization and cost for the Spea2, NSGA2, and Black hole algorithms. Compared with the most existing Figure. 5. Pareto front of AHP base multi objective black hole methods, our approaches which apply AHP on calculating the dominance relation in Black hole are able to meet user’s preferences better. 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