IPDPS’14 Reviewer’s Comments

1. IPDPS’14 Reviewer’s Comments

2. Summary • Typos. • Energy model • Too simple. • Cost function • Should use more standardized cost functions such as the energy-delay product. • Theorems • Single core algorithmic can be found in lots of previous papers. • Proofs for theorem 4 and 5 should be further detailed. • Proof of NP-C for mixed mode does not need that many details.

3. Summary • Scheduling algorithm for mixed mode • A smarter heuristic is needed. • Compare with actual algorithms from the literature as opposed to “baseline” and “adaptive.” • Experimental evaluation • How are the values for E(pk) obtained? How to justify the values for Re and Rt? • Results are not that convincing. • Should explicitly identify what is being implemented on a real system and what is being simulated. • Related works • Major improvement needed.

4. Paper Study • Energy-Efficient Algorithms, May 2010. • Reclaiming the energy of a schedule: models and algorithms, April 2012.

6. Reviewer 1 • The article is, in general, well structured and written. However, the English writing style needs significant improvement and the article contains many grammatical errors and typos. Moreover, the article has some deficiencies.Here are the most obvious ones: • - The energy model used is not clearly described. The article says that "the energy consumption is proportional to the square of the frequency", but this seems to be too simplistic, omitting leakage power of the processor, energy consumption of the memory and peripheral devices. • - The cost function uses the sum of the energy cost and the execution time cost. This is quite unusual. Why do the authors not use more standardized cost functions such as the energy-delay product? • - In the section about the experimental evaluation, some important information is missing. How is the automatic core frequency scaling of Linux disabled? Is the DW-6091 used a normal power-meter (which I suppose)? If so, much more accurate results could be obtained with a specialized power-meter, see the PowerPacktools. • - The experimental evaluation performed is not that convincing. The workload produced with the SPEC benchmarks and the game tasks is synthetic. Since the authors first measured the execution time of the tasks and then assemble them to a synthetic workflow with a small number of tasks, it is not really surprising that the execution time of the workflow can be predicted quite accurately. Moreover, the authors should show the schedule produced. • - The related work section is quite weak. There are many recent research approaches considering scheduling algorithms for DVFS processors, and none of them is cited. Moreover, work on algorithmic aspects of speed scaling is also related and should be cited. Greedy scheduling algorithms have often been proposed. What is the relation to the scheduling algorithms in this article? • In conclusion, I cannot recommend to accept this article.

7. Reviewer 2 • The paper does a good job of analyzing the environment with the batch jobs (especially, the case where tasks do not have deadlines). It was interesting to split the analysis of the problem into two with 1) picking the processing rate for the kth queued job and 2) picking the ordering for the k homogenous jobs. The part about C(k, pk) being independent of the length of the jobs, i.e., Lk was presented well. The optimality of the algorithm developed for this environment was well proved. • The paper lacks in its consideration of the mixed mode environment. The proof of the problem being NP-Complete is performed well but the algorithm developed to solve the problem is not novel. The algorithm just uses earliest-deadline-first and best-fit (and is appropriately named as BEDF+BestFit). Even the earliest-deadline-first just does a binary search to find the least number of cores that can be used for that phase of the algorithm. The algorithm is neither innovative nor efficient. • The experiments section is also lacking in its significance for two reasons. The first is that there is minimal additional significance of implementing in a real environment because (at least the way it is presented) the main difference between the simulation and the real test seems to be that the simulation uses average values of the execution time and energy consumption whereas in the real implementation those values may slightly differ from the average. The second reason is that for both the batch mode and the mixed mode, the author’s algorithms are compared with other algorithms that clearly consider less information and will perform poorly. In addition, the tests with the different Cost Function Coefficients add very little value and are obvious results. • It would be useful if the authors designed a smarter heuristic for the mixed mode environment and compared it to actual algorithms from the literature as opposed to “baseline” and “adaptive.” • Clarify that the environments considered (especially in the mixed mode) are not heterogeneous. • Cite the papers that have the algorithms Half Maximum, Earliest-Deadline-First, and Best-Fit in the appropriate places. • There are plenty of typos in the paper. Kindly review the paper and remove spelling and grammatical mistakes.

8. Reviewer 3 • The single core algorithmics can be found in lots of previous papers, which apparently the authors don't know about. These papers could for example have found by checking the relatively recent CACM survey: Susanne Albers: Energy-efficient algorithms. Com. ACM 53(5): 86-96 (2010). • It seems that Theorem 5 is claiming that the given algorithm is optimal, which is quite unlikely to be correct. • The evaluation section should explicitly identify what is being implemented on a real system and what is being simulated. The authors mix the discussion of implementation/simulation to the point where the reader is not clear about what is being reported. It is not even clear why simulation would be needed in the presence of a real implementation since no analysis of sensitivity to different architecture parameters is provided.

9. Reviewer 4 • These models of tasks are quite simplistics and have probably be studied elsewhere (for example theorems 1 and 2 were already proven in "Reclaiming the energy of a schedule: models and algorithms." by Aupy et al.; Okuma et al. in "Software energy reduction techniques for variable-voltage processors" studied the problem with mixed arrival times), unfortunately this paper lacks related work. • For the batch mode model, the proofs for theorem 4 and 5 are not satisfactory, they should be further detailed. • For the mixed mode model, the NP-completeness proof is simply the proof of NP-completeness of the classical scheduling problem, it does not need that many details. What about on a single machine? • For the evaluation  section:- Table 2, how are the values for E(pk) obtained? While T(pk) is clearly 1/pk, contrary to what was said before, E(pk) is not equal to pk^2.- How do you justify the values for Re and Rt? • For the mixed mode, it is not clear whether the evaluations represented mixed jobs since all jobs are issued at time 0 and expected to be finished by time 10 minutes. • Finally, note that there are many typos throughout the text.