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An Overview of Myrinet

An Overview of Myrinet. By: Ralph Zajac. What is Myrinet?. LAN designed for clusters Based on USCD’s ATOMIC LAN Has many characteristics of MPP message-passing networks. MPP Network Characteristics. High data rate Regular topology and scalability Very low error rate Cut-through routing

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An Overview of Myrinet

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  1. An Overview of Myrinet By: Ralph Zajac

  2. What is Myrinet? • LAN designed for clusters • Based on USCD’s ATOMIC LAN • Has many characteristics of MPP message-passing networks

  3. MPP Network Characteristics • High data rate • Regular topology and scalability • Very low error rate • Cut-through routing • Flow control

  4. ATOMIC LAN: Overview • Based on technology from Caltech’s Mosaic project • Used TCP/IP at burst rates of 400 Mb/s • Error rate less than 10-15

  5. ATOMIC LAN: Limitations • Asynchronous communication could lead to deadlock • Network topology • Complex • Hidden computing power • Performance limited by lack of DMA in host interface • End-to-end data rates limited by TCP/IP stack of OS

  6. Myrinet • Designed to address the limitations of ATOMIC LAN • Not limited to an existing MPP network • Specifications published in ANSI/VITA 26-1998

  7. Myrinet: Links • Can be copper (up to 25m) or optical-fiber • Full duplex • Uses non-return-to-zero encoding • Flow control run by a slack buffer STOP GO Slack Buffer

  8. Myrinet: Packets and Routing • Leading byte determines the outgoing port • MSB of each header byte distinguishes between “host” and “switch” packets • Variable payload length • 8-bit CRC

  9. Myrinet: Switches • Use blocking-cut-through routing • Each contains two custom VLSI chips • crossbar-switch • dual interface • Topology is arbitrary

  10. Myrinet: Host Interface • Available for PCI and Sbus • 32-bit SRAM for MCP • Can act as a slave or a bus master

  11. Myrinet: Software • MCP • Handles all interfacing with the network • Continuously mapping and monitoring the network • Host Software • TCP/IP and UDP/IP • Myrinet API

  12. High Performance Virtual Machine • Windows NT 4.0 cluster built at UCSD and UIUC for the NCSA • 96 dual processor nodes • Used a fat-tree network with 8-port Myrinet switches • Was a 56 GFlops system with: • 45 GB of DRAM • 1.6 MB/s bisection bandwidth • 400 GB of disk storage

  13. HPVM: Testing • Tested on four programs • ZeusMP: astrophysical phenomena in 3D • Cactus: modular 3D numerical relativity • AS-PCG kernel: linear systems solver • QMC kernel: Quantum Monte Carlo simulator • Compared with a Cray T3E and an Origin 2000

  14. HPVM: Results • Performed from 2 to 4 times slower • Slower floating point calculations • Flow control limitations of Myrinet • Much better price/performance ratio

  15. Conclusions • Myrinet is: • Flexible • Fast • Affordable systems with acceptable performance

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