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Large-scale parallel execution of urban-scale traffic simulation and its performance on K computer

  • Daigo UmemotoEmail author
  • Nobuyasu Ito
Research Article
  • 13 Downloads

Abstract

We attempt to perform many-case urban-scale traffic simulations by performing massive parallel computing using K computer, and CARAVAN job manager. We obtain 1025 variations of simulation results with the same condition and different random seeds within 13 h. Each of simulation runs took about 6 h, which is twice longer than the case of using conventional workstations or clusters, and our approach allows further massive parallel computation. The performance and limitations when using K computer are discussed.

Keywords

Traffic flow High-performance computing Multi agent social simulation 

Introduction

In this new era of so-called big data and machine learning, a hope is emerging that we can establish a unified and quantitative sociology in these decades. However, as results of big-data analyses in the past decade, we are already beginning to realize that big data is not sufficiently big since their size is too limited to exhaustively cover the huge parameter space that social phenomena should have, and particularly, often their coverage is biased and makes it difficult to analyze in our interests.

Simulation approach shall be valid to overcome this defect. As pointed out in [1], Multiagent Social Simulation (MASS) is now attracting attention as a powerful methodology of research on social science. Together with the high-performance computing, exhaustive data construction is possible: we can virtually conduct many-case social experiments and deal with them on statistical basis, which has been difficult to conduct in the real world.

For quantitative and rigorous simulation research, the elementary behavior of each agent obey is desired to be rigidly and quantitatively established. Here, the traffic model on straight single lane is well understood in the context of MASS. With the expectation that the results of traffic simulation as a MASS are going to contain some features that closely resembles the actual traffic flow as pointed out in [2], we attempt to construct a simulation system that provides many-case results using K computer.

Our traffic simulation system using K computer

To construct urban-scale traffic simulation system, we use agent-based and open-source simulator SUMO (Simulation of Urban MObility, [3]). We also introduce available digitized map of Kobe city in Japan into the system, which was edited as mentioned in [4] from a digital road map produced by ZENRIN CO., LTD. More detailed simulation conditions are mentioned in [5]. Each simulation with this setup takes about 2–3 h of real time, using Intel (R) Xeon (R) CPU E5-1620 @ 3.60 GHz. The size of the result files is about 2 GB which includes all the intermediate files to enable trial and error offline analysis after the simulations.

To make use of high-performance computing, hence execute exhaustive many-case simulations explained above in parallel, an efficient job manager is required. We use an open-source job manager framework CARAVAN [7] created by our team in purpose of large-scale parameter-space exploration which requires using high-performance computer including K computer. It allows massive parallel execution of the simulation run instances with different parameters and random seeds each other.

In our setup, each instance takes a single process and is isolated. Hence there is no inter-process communication which sometimes becomes a bottle neck of computation speed. CARAVAN also allows to sequentially execute one simulation run after another within a given wall time; we do not use this feature at this stage and finish the entire calculation when the single simulation run instance with longest computation time is completed.

We implemented exactly the same simulation conditions explained above and re-compiled SUMO source code so that it can be entirely executed on K computer. The schematic diagram of entire system and data flow is drawn in Fig. 1. It requires stage-in procedure in the beginning of the calculation, and stage-out procedure in the end of the calculation to fetch the results, because the global file system of computation node of K computer is provided only for computation, not for data storage purpose. All files existing in the computation node during the computation will be entirely deleted when the submitted job finishes. Log-in node is provided for storage purpose instead.
Fig. 1

Entire system of exhaustive simulation system using CARAVAN and K computer

In our setup, input files and executives have the size of about 250 MB in total and result files have the size of about 2 GB on each instance. Soon after the stage-in, the computation starts if enough space in computational resource is available on K computer. Otherwise, we have to wait until assigned calculation start time. This happens when we demand large number of node usage, therefore it is convenient to demand smallest node number available many times and gather up them later on. The smallest node number is 12.

We assign single CPU on each simulation run instance. Each node has eight CPUs, and they share the same file system hence the disk capacity is also shared. The maximum can be set for 29 GB by adding following line in the submitted job script:

#PJM --rsc-list "node-quota=29 GB"

otherwise, the default maximum limitation 14 GB is used. When calculation finishes, each process owns files with size of about 4.5 GB in total finally, consisting of 250 MB of compressed simulation system package, 250 MB of decompressed package, 2 GB of raw result, and 2 GB of compressed result to be staged out in the following process. We chose to use five CPUs in each node to surpress total file size under the 29 GB of limitation, as well as based on the test result to attempt using six CPUs which caused disk full failure. The number of CPUs shall be increased by suppressing the intermediate files, when our analysis becomes sophisticated.

Performance result of large-scale simulation using K computer

Job execution time result provided by K computer is shown in Table 1. There is a tendency that larger demand of number of runs require longer waiting time till the beginning of the execution. When we attempted to submit jobs containing more than 1200 runs, the waiting time exceeded more than two days. However, smaller jobs shown in Table 1 have affordable waiting time. K computer allows users to submit 15 jobs at a time. We made a strategy to use this feature to submit smallest jobs whose run number is 58, and obtained 1052 simulation results with different random seeds and the same simulation parameter within 13 h. With different parameters, the execution time may vary. Mixing up simulations with different parameter may cause the unused resource to be larger, therefore we suggest to submit simulations with the same parameter and different seeds at once.
Table 1

Execution time

Job ID

Number of runs

Submission time

Wait

Execution

Finish time

7497111

118

2018/09/02 02:38:57

1:58:06

6:00:31

10:37:34

7497114

238

2018/09/02 02:41:53

8:10:25

5:53:12

16:45:30

7497122

58

2018/09/02 02:52:57

0:02:36

6:05:26

09:00:59

7497123

58

2018/09/02 02:53:48

0:03:08

6:11:06

09:08:02

7497146

58

2018/09/02 05:19:48

0:02:51

5:58:01

11:20:40

7497147

58

2018/09/02 05:19:51

0:02:48

5:57:56

11:20:35

7497148

58

2018/09/02 05:19:53

0:02:46

6:00:37

11:23:16

7497149

58

2018/09/02 05:24:09

0:26:21

6:05:08

11:55:38

7497150

58

2018/09/02 05:24:11

0:04:55

6:01:25

11:30:31

7497151

58

2018/09/02 05:24:12

3:07:13

5:49:59

14:21:24

7497152

58

2018/09/02 05:24:13

3:07:12

6:02:00

14:33:25

7497153

58

2018/09/02 05:24:14

3:07:12

5:52:41

14:24:07

7497154

58

2018/09/02 05:24:22

1:51:52

5:53:15

13:09:29

7497156

58

2018/09/02 05:24:24

3:53:05

5:59:08

15:16:37

As shown in the table, entire computation time which includes stage-in and out takes about 6 hours. This is not affected by number of simulation run instances or even shorter with larger number of instances because all processes are independently and parallelly executed. Stage-in procedure takes about 30 s and stage-out procedure takes about 7 min which is negligible to the entire processing time. Therefore, the longest computation time of single simulation run instance is about 6 h, which is almost twice the longer than using the conventional CPU. This is because K computer consists of Fujitsu SPARC64 VIIIfx CPU architecture which has almost half clock frequency compared to the conventional CPU architecture, which ensures the stable operation. However, the number of parallel instances is massively larger than conventional workstations or clusters and it is affordable to attempt further larger parallel execution. For example, a cluster with 100 cores requires about 60 h of computation time to finish the same amount of task.

Job management result of job ID 7497156 provided by CARAVAN is shown in Fig. 2. The vertical and horizontal axes represent computation time in seconds since the beginning of each simulation run, and process IDs, respectively. There is an fluctuation in computation time which is within 20,000 s. This is about 10% of the entire time of runs. The white region represents the time space that CPUs are allocated but unused, which is undesirable. We will make use of these by optimizing the node usage in some way in future research.
Fig. 2

Job management result

References

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Copyright information

© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.RIKEN Center for Computational SciencesKobeJapan
  2. 2.Department of Applied Physics, Graduate School of EngineeringThe University of TokyoTokyoJapan

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