1. Many Integrated Core Prototype PRACE Autumn School 2012 on Massively Parallel Architectures and Molecular Simulations Sofia, 24-28 September 2012 G. Erbacci – CINECA

2. Outline HPC evolution The Eurora Prototype MIC architecture Programming MIC 2

3. Many Integrated Core Prototype HPC evolution The Eurora Prototype MIC architecture Programming MIC 3

4. HPC at CINECA CINECA: National Supercomputing Centre in Italy manage the HPC infrastructure provide support to Italian and European researchers promote technology transfer initiatives for industry CINECA is a Hosting Member in PRACE –PLX: Cluster Linux with GPUs (Tier-1 in PRACE) –FERMI: IBM BG/Q (Tier-0 in PRACE) 4

5. PLX@CINECA IBM Cluster linux Processor type: 2 six-cores Intel Xeon (Esa-Core Westmere) X 5645 @ 2.4 GHz, 12MB Cache N. of nodes / cores: 274 / 3288 RAM: 48 GB/Compute node (14 TB in total) Internal Network: Infiniband with 4x QDR switches (40 Gbps) Acccelerators: 2 GPUs nVIDIA M2070 per node 548 GPUs in total Peak performance: 32 Tflops 565 TFlops SP GPUs 283 TFlops DP GPUs 5

6. FERMI@CINECA Architecture: 10 BGQ Frames Model: IBM-BG/Q Processor type: IBM PowerA2 @1.6 GHz Computing Cores: 163840 Computing Nodes: 10240 RAM: 1GByte / core (163 PByte total) Internal Network: 5D Torus Disk Space: 2PByte of scratch space Peak Performance: 2PFlop/s N. 7 in Top 500 rank (June 2012) National and PRACE Tier-0 calls 6

7. CINECA HPC Infrastructure 7

8. Computational Sciences Computational science (with theory and experimentation), is the “third pillar” of scientific inquiry, enabling researchers to build and test models of complex phenomena Quick evolution of innovation: - Instantaneous communication - Geographically distributed work - Increased productivity - More data everywhere - Increasing problem complexity - Innovation happens worldwide 8

9. Technology Evolution More data everywhere: Radar, satellites, CAT scans, sensors, micro-arrays weather models, the human genome. The size and resolution of the problems scientists address today are limited only by the size of the data they can reasonably work with. There is a constantly increasing demand for faster processing on bigger data. Increasing problem complexity Partly driven by the ability to handle bigger data, but also by the requirements and opportunities brought by new technologies. For example, new kinds of medical scans create new computational challenges. HPC Evolution As technology allows scientists to handle bigger datasets and faster computations, they push to solve harder problems. In turn, the new class of problems drives the next cycle of technology innovation. 9

10. Top 500: some facts 1976 Cray 1 installed at Los Alamos: peak performance 160 MegaFlop/s (10 6 flop/s) 1993 (1° Edition Top 500) N. 1 59.7 GFlop/s (10 12 flop/s) 1997 Teraflop/s barrier (10 12 flop/s) 2008 Petaflop/s (10 15 flop/s): Roadrunner (LANL) Rmax 1026 Gflop/s, Rpeak 1375 Gflop/s hybrid system: 6562 processors dual-core AMD Opteron accelerated with 12240 IBM Cell processors (98 TByte di RAM) 2012 (J) 16.3 Petaflop/s : Lawrence Livermore’s Sequoia Supercomputer BlueGene/Q, (1.572.864 cores) - 4 European systems in the Top 10 - Total combined performance of all 500 systems has grown to 123.02 Pflop/s, compared to 74.2 Pflop/s six months ago - 57 systems use accelerators - - - - Toward Exascale 10

11. Dennard Scaling law (MOSFET) L’ = L / 2 V’ = V / 2 F’ = F * 2 D’ = 1 / L 2 = 4D P’ = P do not hold anymore! The power crisis! L’ = L / 2 V’ = ~V F’ = ~F * 2 D’ = 1 / L 2 = 4 * D P’ = 4 * P The core frequency and performance do not grow following the Moore’s law any longer CPU + Accelerator to maintain the architectures evolution In the Moore’s law Programming crisis! 11

12. Roadmap to Exascale (architectural trends) 12

13. Heterogeneous Multi-core Architecture Combines different types of processors –Each optimized for a different operational modality Performance –Synthesis favors superior performance For complex computation exhibiting distinct modalities Purpose-designed accelerators –Integrated to significantly speedup some critical aspect of one or more important classes of computation –IBM Cell architecture, ClearSpeed SIMD attached array processor, Conventional co-processors –Graphical processing units (GPU) –Network controllers (NIC) –Many Integrated Cores (MIC ) –Efforts underway to apply existing special purpose components to general applications 13

14. Accelerators A set (one or more) of very simple execution units that can perform few operations (with respect to standard CPU) with very high efficiency. When combined with full featured CPU (CISC or RISC) can accelerate the “nominal” speed of a system. CPUACC. CPU ACC. Physical integration CPU & ACC Architectural integration Single thread perf. throughput 14

15. nVIDIA GPU Fermi implementation packs 512 processor cores 15

16. ATI FireStream, AMD GPU 2012 New Graphics Core Next “GCN” With new instruction set and new SIMD design 16

17. Intel MIC (Knight Ferry) 17

18. Real HPC Crisis is with Software A supercomputer application and software are usually much more long-lived than a hardware - Hardware life typically four-five years at most. - Fortran and C are still the main programming models Programming is stuck - Arguably hasn’t changed so much since the 70’s Software is a major cost component of modern technologies - The tradition in HPC system procurement is to assume that the software is free. It’s time for a change - Complexity is rising dramatically - Challenges for the applications on Petaflop systems - Improvement of existing codes will become complex and partly impossible - The use of O(100K) cores implies dramatic optimization effort - New paradigm as the support of a hundred threads in one node implies new parallelization strategies - Implementation of new parallel programming methods in existing large applications has not always a promising perspective There is the need for new community codes 18

19. What about parallel App? In a massively parallel context, an upper limit for the scalability of parallel applications is determined by the fraction of the overall execution time spent in non-scalable operations (Amdahl's law). maximum speedup tends to 1 / ( 1 − P ) P= parallel fraction 1000000 core P = 0.999999 serial fraction= 0.000001 19

20. Trends Vector Distributed memory Shared Memory Hybrid codes MPP System, Message Passing: MPI Multi core nodes: OpenMP Accelerator (GPGPU, FPGA): Cuda, OpenCL Scalar Application 20

21. Many Integrated Core Prototype HPC evolution The Eurora Prototype MIC architecture Programming MIC 21

22. EURORA Prototype 22 Evolution of AURORA architecture by Eurotech (http://www.eurotech.com/)http://www.eurotech.com/ –Aurora Rack: 256 Nodes: 512 CPUs –101 Tflops @ 100 KW –liquid cooled CPU: Xeon Sandy Bridge (SB) –Up to One full cabinet (128 nodes + 256 accelerators) Accelerator: Intel Many Integrated Cores (MIC) Network architecture: IB and Torus interconnect –Low Latency/High Bandwidth Interconnect Cooling: Hot Water

23. EURORA chassis 1 rack, 16 chassis 16 nodes card or 8 nodes card + 16 accelerators Eurora Rack  Physical dimensions: 2133mm(48U) h, 1095mm w, 1500 mm d;  Weight (full rack with cooling fully loaded with water): 2000Kg  Power/Cooling typical requirements: 120-130 kW @ 48 Vdc 23

24. EURORA node  2 Intel Xeon E5  2 Intel MIC or  2 nVidia Kepler  16GByte DDR3 1.6GHz  SSD disk 24

25. Node card mockup 25 Presented at ISC12 Can host MIC and K20 cards Thermal analysis and validation performed

26. EURORA Network 3D Torus custom network FPGA (Altera Stratix V) EXTOLL, APENET Ad-hoc MPI subset InfiniBand FDR Mellanox ConnectX3 MPI + Filesystem Synch 26

27. Cooling Hot water 50-80C Temperature gap 3-5C No rotating fans Cold plates –direct on component liquid cooling Dry chillers Free cooling Temperature sensors – downgrade performance is required System isolation Quick disconnect 27

28. 28 EURORA prototype (Node Accelerator) EURopean many integrated cORe Architecture Goal: evaluate a new architecture for next generation Tier-0 system Partners: - CINECA, Italy - GRNET, Greece - IPB, Serbia - NCSA, Bulgaria Vendor: Eurotech, Italy

29. EURORA Installation Plan 29

30. HW Procurement Contract with EUROTECH signed in July –64 compute card –128 Xeon SandyBridge 3.1GHz –16GByte DDR3 1600MHz per node –160GByte SSD per node –1 FPGA (Altera Stratix V) per node –IB FDR –128 Accelerator cards INTEL KNC (or NVIDA K20) –Thermal sensors network 30

31. HW Procurement and Facility Contract with EUROTECH signed in July Integration in the Facility –First assessment of the location with EUROTECH in May –First project of integration completed Estimated cost higher than budgeted –Second assessment with EUROTECH in September (before the end) –Procurement of the technology: Dry coolers, pipes and pumps, exchanger, tanks, filters 31

32. Some Applications www.quantum-espresso.org www.gromacs.org 32

33. EURORA Programming Models Message Passing (MPI) Shared Memory (OpenMP, TBB) MIC offload (pragmas) / native Hybrid: MPI + OpenMP + MIC extensions/OpenCL 33

34. ACCELERATORS First K20 and KNC (dense form factor) samples in September KNC standard expansion module, already available to start the work on software. 34

35. 35 Installation of the KNC software kit Test of the compiler, and node card HW First simple (MPI+OpenMP) application test First Mic-to-Mic MPI communication test –Intel MPI –within the same node Test of the affinity Software

36. ACCESS Access will be granted upon request to the partners of the prototype project. Other requests will be evaluated case by case. We are working to grant early access to the KNC board already installed. 36

37. Expected results Validate node card design; Density in the order of 500TFlops/rack (BG/Q is 200TFlops/rack); 3D Torus network scalability and performance vs InfiniBand; Power Usage Effectiveness (PUE) close to or less than 1.1 (free cooling most of the year); Programming model for MIC accelerator; improved applications efficiency with respect of multi-core clusters; Bridge the gap with exascale machines 37

38. Many Integrated Core Prototype HPC evolution The Eurora Prototype MIC architecture Programming MIC 38

39. MIC Architecture MIC Many Integrated Core Knight Corner co-processor Intel Xeon Phi co-processor –22 nm technology –> 50 Intel Architecture cores –connected by a high performance on-die bi-directional interconnect. –I/O Bus: PCIe –Memory Type: GDDR5 and >2x bandwidth of KNF –Memory size: 8 GB GDDR5 memory technology –Peak performance: >1 TFLOP (DP) –Single Linux image per chip 39

40. MIC Intel Xeon Phi Ring 40 Each microprocessor core is a fully functional, in-order core capable of running IA instructions independently of the other cores. Hardware multi-threaded cores Each core can concurrently run instructions from four processes or threads. The Ring Interconnect connecting all the components together on the chip

41. The Processor Core 41 - Fetches and decodes instructions from four hardware thread execution contexts - Executes the x86 ISA, and Knights Corner vector instructions - The core can execute 2 instructions per clock cycle, one per pipe - 32KB, 8-Way set associative L1 Icache and Dcache - Core Ring Interface (CRI) - L2 Cache - Memory controllers (which access external memory devices to read and write data) - PCI Express client: is the system interface to the host CPU or PCI Express switch,

42. The vector processing unit 42 Vector processing unit (VPU) associated with each core. This is primarily a sixteen-element wide SIMD engine, operating on 512-bit vector registers. Gather / Scatter Unit Vector Mask

43. 43 Vector processing do i = 1, N A(i) = B(i)+C(i) end do V0  V1 + V2 Functional Unit Add Floating Point

44. The L2 Cache Each core has a 512 KB L2 cache The L2 cache is part of the Core-Ring Interface block The L2 cache is private to the core: each core acts as a stand-alone core with 512 KB of total L2 cache space Other cores can not directly use them as a cache 512 KB x > 50 cores  > 25 MB L2 on Knight Corner Tag Directory on each core, not private to the core A simplified way to view the many cores in Knights Corner is as a chip-level symmetric multiprocessor (SMP) and > 50 such cores share a high-speed interconnect on-die. 44

45. The Ring Interconnect Knights Corner has 10 rings (5 in each direction): –BL ring carries the data –2 AR rings carry address –2 AK rings carry coherence information Knights Corner can send data across the ring once per clock per controller 45

46. Many Integrated Core Prototype HPC evolution The Eurora Prototype MIC architecture Programming MIC 46

47. Compute modes vision 47 Xeon CentricMIC Centric Xeon Hosted Scalar Co-processing SymmetricParallel Co-processing MIC Hosted General purpose serial and parallel computing Codes with balanced needs Highly-parallel codes Highly parallel codes with scalar phases Codes with highly- parallel phases

48. 48 Main( ) Foo( ) MPI_*( ) Main( ) Foo( ) MPI_*( ) Foo( ) Main( ) Foo( ) MPI_*( ) Xeon PCIe MIC Foo( ) Main( ) Foo( ) MPI_*( ) Main( ) Foo( ) MPI_*( ) Main( ) Foo( ) MPI_*( ) Xeon NativeMIC NativeMIC-hosted Xeon co- processed Autonomous Mode Xeon-hosted MIC Co- processed Offload: Intel C, C++, Fortran Compiler Native: -mmic

49. MPI programmming models for MIC 49

50. Offload Model 50 This model is characterized by the MPI communications taking place only between the host processors. The co-processors are used exclusively thru the offload capabilities of the products like Intel® C, C++, and Fortran Compiler for Intel MIC Architecture, Intel Math Kernel Library (MKL), etc. This mode of operation is already supported by the Intel MPI Library for Linux OS MPI on Host Devices with Offload to Co-processors

51. Symmetric Model 51 The MPI processes reside on both the host and the MIC devices This model involves both the host CPUs and the co-processors into the execution of the MPI processes and the related MPI communications. Message passing is supported inside the co-processor, inside the host node, and between the co-processor and the host. environment variable Most general MPI view of an essentially heterogeneous cluster.

52. Co-processor-only Model (or MPI Native) 52 the MPI processes reside on the MIC co- processor only. MPI libraries, the application, and other needed libraries are uploaded to the co- processors. An application can be launched from the host or the co-processor. This can be seen as a specific case of the symmetric model

53. 53

54. 54 3D Eulerian chemical-transport model (CTM); Fortran 77/90; Used to study the transport, chemical conversion and deposition of atmospheric pollutants; Manages multiple nested grids with different resolution. Can be compiled in four different ways: - Serial; - OpenMP; - MPI (Master-Worker strategy); - Hybrid (OpenMP + MPI). Good candidate to be tested on MIC Native compilation: All FARM processes run on the MIC. Symmetric compilation: Master process runs on the host; Worker Processes run on the MIC. FARM: Air quality Model

55. 55 Native compilation

56. 56 Native compilation

57. 57 Porting on MIC Pros: Compilation with an additional Intel compiler flag (-mmic); Scalability tests: fast and smooth; Quick analysis with Intel tools (VtuneT, Itac Intel Trace Analyzer and Collector; Porting time: one day with validation of the numerical result; expert developer of FARM, with good knowledge of the Intel compiler, BUT with only a basic knowledge of MIC. Best scalability with OpenMP and Hybrid. Cons: MPI Init routine problem: increasing CPU time for increasing number of processes; Same problem when using two MICs together; Detailed analysis of OpenMP threads is currently not available; Execution time depends strongly from code vectorization, so compiler vectorization skills and code structure are a key point to have a vectorizable satisfactory overall performances.

58. Conclusions Hybrid clusters can bridge the gap with exascale machines Test and monitor technologies that could influence the design of Exascale systems Introduce fault tolerance at system and application level New hybrid programming models –Focus on the applications –Big Data Challenge –Uncertainties Challenge –coupling Architecture-Algorithm-Application 58