Designing a PC Farm to Simultaneously Process Separate Computations Through Different Network Topologies Patrick Dreher MIT

A Multi-Purpose PC Farm Goals of the Project Functionality and Constraints Hardware Selection Software Selection Operation

Goals of the Project User requirements Production machine for the experimentalists for Monte Carlo simulations and physics analysis of experimental data Development and testing platform for the theorists to examine the performance characteristics of the x86 chip design Design a way for both experimentalists and theorists to peacefully co-exist sharing the existing PC farm hardware at the same time

Existing PC Farm Hardware The configuration for each machine in the existing PC farm 20 dual Pentium II 400 MHz CPUs 384 Mbytes memory 13 Gbytes disk space fast Ethernet PCs interconnected by Kingston EtherRx 100 BaseTx fast Ethernet stackable hubs A front end PC connecting the farm nodes to the internet

PC Farm Software Operating system is RedHat Linux x86 version 5.2 Linux kernel configured for SMP operations Production of batch jobs managed through Network Queuing System (http://www.gnqs.org)

LAN HUB

Constraints for the Project No new funds were available to purchase additional CPUs for the existing PC farm No new funds were available to purchase a separate PC farm for development and testing of theory codes No funds were available at the level needed to purchase high performance network switches (such as Myrinet) Small amounts of funds were available for additional peripherals

Modified PC Farm - Functionality Original configuration had 20 machines (40 CPUs) available under a batch queuing system (NQS) Modified configuration set aside 4 of the machines for the theorists (8 CPUs) leaving the other 32 CPUs for production work and analysis of experimental data Four 4-port Adaptec network cards were purchased and one was installed in each of the four machines The four machines were networked together in a two-dimensional torus

LAN HUB

Modes of Operation Production operation for the experimentalists involved configuring NQS so that it identified 40 CPUs available for production and analysis of data An alternate NQS configuration was built that identified only 32 CPUs available for production Only one of these two configurations could be installed and operational on the PC farm at a given time

Modes of Operation (cont’d) When the alternate NQS configuration was loaded Experimentalists would continue to use the 32 CPUs The theorists would first log onto the front end and then use ssh to log onto one of the 4 machines not grouped under the alternate NQS configuration From this point, theory codes could be started using one, two, or all four machines

Results Theorists - Experimentalists Gathered data as part of a larger program to compare the performance between x86, alpha 164 and 264 chips Interprocessor communication using MPI Tests on memory bandwidth Tests on lattice size of versus L2 cache for certain computation routines Experimentalists continued Monte Carlo production and analysis of experimental data

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