Memory balancing for large-scale network simulation in power -law networks

Kim, HyoJeong. Ph.D., Purdue University, December 2008. Memory Balancing for Large-scale Network Simulation in Power-law Networks. Major Professor: Kihong Park. Large-scale network simulation has grown in importance due to a rapid increase in Internet size and the availability of Internet measurement topologies with applications to computer networks and network security. A key obstacle to large-scale network simulation over PC clusters is the memory balancing problem, where a memoryoverloaded machine can slow down a distributed simulation due to disk I/O overhead. Network partitioning methods for parallel and distributed simulation are insufficiently equipped to handle new challenges brought on by memory balancing due to their focus on CPU and communication balancing. This dissertation studies memory balancing for large-scale network simulation in power-law networks over PC clusters. First, we design and implement a measurement subsystem for dynamically tracking memory consumption in DaSSFNet, a distributed network simulator. Accurate monitoring of memory consumption is difficult due to complex protocol interaction through which message related events are created and destroyed inside and outside a simulation kernel. Second, we achieve efficient memory cost monitoring by tackling the problem of estimating peak memory consumption of a group of simulated network nodes in power-law topologies during network partitioning. In contrast to CPU balancing where the processing cost of a group of nodes is proportional to their sum, in memory balancing this closure property need not hold. Power-law connectivity injects additional complications due to skews in resource consumption across network nodes. Third, we show that the maximum memory cost metric outperforms the total cost metric for memory balancing under multilevel rexv cursive partitioning but the opposite holds for CPU balancing. We show that the trade-off can be overcome through joint memory-CPU balancing—in general not feasible due to constraint conflicts—which is enabled by network simulation having a tendency to induce correlation between memory and CPU costs. Fourth, we evaluate memory balancing in the presence of virtual memory (VM) management which admits larger problem instances to be run over limited physical memory. VM introduces complex memory management dependencies that make understanding and evaluating simulation performance difficult. We provide a performance evaluation framework wherein the impact of memory thrashing in distributed network simulation is incorporated which admits quantitative performance comparison and diagnosis. Fifth, we show that improved memory balancing under the maximum cost metric in the presence of VM manifests as faster completion time compared to the total cost metric despite the CPU balancing advantage of the latter. In the cases where the CPU balancing advantage of the total cost metric is strong, we show that joint memory-CPU balancing can achieve the best of both worlds. We carry out performance evaluation using benchmark applications with varying traffic characteristics: BGP routing, worm propagation under local and global scanning, and distributed client/server system. We use a testbed of 32 Intel x86 machines running a measurement-enhanced DaSSFNet over Linux.