Browsing by Author "Mergenci, Cem"

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Open Access
AutopaR: An Automatic Parallelization Tool for Recursive Calls
(IEEE, 2014-09) Kalender, Mert Emin; Mergenci, Cem; Öztürk, Özcan
Manycore systems are becoming more and more powerful with the integration of hundreds of cores on a single chip. However, writing parallel programs on these manycore systems has become a problem since the amount of available parallel tools and applications are limited. Although exploiting parallelism in software is possible, it requires different design decisions, significant programmer effort and is error prone. Different libraries and tools try to make the transition to parallelism easier, however there is no concrete system to make it transparent to software developer. To this end, our proposed tool is a step forward to improve the current state. Our approach, Autopar, specifically aims at achieving automatic parallelization of recursive applications using static program analysis. It first decides on the recursive functions of a given program. Then, it performs analysis and collects information about these recursive functions. Our analysis module automatically collects program information without requiring any modification in the program design or developer involvement. Finally, it achieves automatic parallelization by introducing necessary OpenMP pragmas in appropriate places in the application. © 2014 IEEE.
Open Access
Fly-path: Traffic-based multi-hop routing approach for hybrid wireless data centers
(Elsevier BV, 2021-03-15) Mergenci, Cem; Körpeoğlu, İbrahim
High data transfer rates achieved by 802.11ad at 60 GHz ISM band enables use of wireless communication in data centers. In this paper, we investigate the possibility of offloading traffic from wired to wireless network in hybrid data centers. By understanding the capabilities of the wireless network, we can design the hybrid data center network accordingly, to achieve better construction and operating efficiency. First, we propose a system model in which each top-of-the-rack switch is equipped with two radios, so that three non-overlapping channels of 802.11ad that are available worldwide can be assigned in an interference-free manner to any configuration of wireless links. Then, we propose multi-hop routing algorithms that assign traffic to wireless infrastructure. These algorithms consist of two families. SP family of algorithms route traffic only over shortest-paths between source and destination pairs. LP algorithms relax this restriction and assign traffic to longer paths when necessary. In order to evaluate the performance of our routing algorithms, we also propose a random data center traffic generation method, based on an analysis of a real-world data center traffic pattern. We evaluate the performance of our allocation methods in terms of different metrics for various network sizes. Results show that our methods can offload significant amount of traffic from wired to wireless network, can achieve quite high throughput, and can utilize wireless links very well.
Open Access
Generic resource allocation metrics and methods for heterogeneous cloud infrastructures
(Elsevier, 2019) Mergenci, Cem; Körpeoğlu, İbrahim
With the advent of cloud computing, computation has become a commodity used by customers to access computing resources with no up-front investment, but as an on-demand and pay-as-you-go basis. Cloud providers make their infrastructure available to public so that anyone can obtain a virtual machine (VM) instance that can be remotely configured and managed. The cloud infrastructure is a large resource pool, allocated to VM instances on demand. In a multi-resource heterogeneous cloud, allocation state of the data center needs to be captured in metrics that can be used by allocation algorithms to make proper assignments of virtual machines to servers. In this paper, we propose two novel metrics reflecting the current state of VM allocation. These metrics can be used by online and offline VM placement algorithms in judging which placement would be better. We also propose multi-dimensional resource allocation heuristic algorithms showing how metrics can be used. We studied the performance of proposed methods and compared them with the methods from the literature. Results show that our metrics perform significantly better than the others and can be used to efficiently place virtual machines with high success rate.
Open Access
Routing in delay tolerant networks with periodic connections
(2010) Mergenci, Cem
In delay tolerant networks (DTNs), the network may not be fully connected at any instance of time, but connections occurring between nodes at di erent times make the network connected through the entire time continuum. In such a case, traditional routing methods fail to operate as there are no contemporaneous end-to-end paths between sources and destinations. This study examines the routing in DTNs where connections arise in a periodic nature. Various levels of periodicity are analyzed to meet requirements of di erent network models. We propose various routing algorithms for periodic connections. Our proposed methods can nd routes that can guarantee earliest delivery and minimum hop count. We evaluate our routing schemes via extensive simulation experiments and also compare them to some other popular routing approaches proposed for delay tolerant networks. Our evaluations show the feasibility and e ectivenes of our schemes as alternative routing methods for delay tolerant networks.
Open Access
Server and wireless network resource allocation strategies in heterogeneous cloud data centers
(2020-08) Mergenci, Cem
Resource allocation is one of the most important challenges in operating a data center. We investigate allocation of two main types of resources: servers and network links. Server resource allocation problem is the problem of how to allocate virtual machines (VMs) to physical machines (PMs). By modeling server resources (CPU, memory, storage, IO, etc.) as a multidimensional vector space, we present design criteria for metrics that measure the fitness of an allocation of VMs into PMs. We propose two novel metrics that conform to these design criteria. We also propose VM allocation methods that use these metrics to compare allocation alternatives when allocating a set of VMs into a set of PMs. We compare performances of our proposed metrics to the ones from the literature using vector bin packing with heterogeneous bins (VBPHB) benchmark. Results show that our methods find feasible solutions to a greater number of allocation problems than the others. Network resource allocation problem is examined in hybrid wireless data centers. We propose a system model in which each top-of-the-rack (ToR) switch is equipped with two radios operating in 60-GHz band using 3-channel 802.11ad. Given traffic flows between servers, we allocate wireless links between ToR switches so that the traffic carried over the wireless network is maximized. We also present a method to randomly generate traffic based on a real data center traffic pattern. We evaluate the performance of our proposed traffic allocation methods using randomly generated traffic. Results show that our methods can offload significant amount of traffic from wired to wireless network, while achieving low latency, high throughput, and high bandwidth utilization.