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konecny-hpa-xmt

konecny-hpa-xmt - Introducing the Cray XMT Petr Konecny...

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Unformatted text preview: Introducing the Cray XMT Petr Konecny November 29 th 2007 November 07 Slide 2 Agenda ¡ Shared memory programming model • Benefits/challenges/solutions ¡ Origins of the Cray XMT ¡ Cray XMT system architecture • Cray XT infrastructure • Cray Threadstorm processor ¡ Basic programming environment features ¡ Examples • HPCC Random Access • Breadth first search ¡ Rules of thumb ¡ Summary November 07 Slide 3 Shared memory model ¡ Benefits • Uniform memory access • Memory is distributed across all nodes • No (need for) explicit message passing • Productivity advantage over MPI ¡ Challenges • Latency: time for a single operation • Network bandwidth limits performance • Legacy MPI codes November 07 Slide 4 Addressing shared memory challenges ¡ Latency • Little’s law: ¡ Parallelism is necessary ! ¡ Concurrency = Bandwidth * Latency ¡ e.g.: 800 MB/s, 2 μ s latency => 200 concurrent 64-bit word ops • Need a lot of concurrency to maximize bandwidth ¡ Concurrency per thread (ILP, vector, SSE) => SPMD ¡ Many threads (MTA, XMT) => MPMD ¡ Network Bandwidth • Provision lots of bandwidth ¡ ~1 GB/s per processor, ~5 GB/s per router on XMT • Efficient for small messages • Software controlled caching (registers, nearby memory) ¡ Eliminates cache coherency traffic ¡ Reduces network bandwidth November 07 Slide 5 rigins of the Cray XMT Multithreaded Architecture (MTA) Shared memory programming model Thread level parallelism Lightweight synchronization Cray XT Infrastructure Scalable I/O, HSS, Support Network efficient for small messages Cray XMT (a.k.a. Eldorado) Upgrade Opteron to Threadstorm November 07 Slide 6 Cray XMT System Architecture MTK Linux Compute Service & IO RAID Controllers Network PCI-X 10 GigE Fiber Channel PCI-X Service Partition • Linux OS • Specialized Linux nodes Login PEs IO Server PEs Network Server PEs FS Metadata Server PEs Database Server PEs Compute Partition MTK (BSD) November 07 Slide 7 Cray XMT Speeds and feeds Threadstorm...
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konecny-hpa-xmt - Introducing the Cray XMT Petr Konecny...

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