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Intel Multi-Core Technology
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  1. Intel Multi-Core Technology

  2. Intel Multi-Core Technology • New Energy Efficiency by Parallel Processing • Multi cores in a single package • Second generation high k + metal gate 32nm Technology • Intel Turbo Boost technology • Changing frequency depending on workload • Intel Hyper-Threading Technology • Two threads on a single core • Tera-scale computing • Intend to scale multi-core to 100 cores and beyond

  3. Multi-Core Hyper-Thread • Multi-core chips allow 2 or more cores on a single package on a computer. • Multi-core chips do more work per clock cycle, running at lower clock frequency. • Hyper-thread allows efficient use of a single processor • by allowing multiple threads to share the core’s resources

  4. Interaction with theOperating System • OS perceives each core as a separate processor • OS scheduler maps threads/processes to different cores • Most major OS support multi-core today:Windows, Linux, Mac OS X, …

  5. Why multi-core ? • Difficult to make single-coreclock frequencies even higher • Deeply pipelined circuits: • heat problems • speed of light problems • difficult design and verification • large design teams necessary • server farms need expensiveair-conditioning • Many new applications are multithreaded • General trend in computer architecture (shift towards more parallelism)

  6. Instruction-level parallelism • Parallelism at the machine-instruction level • The processor can re-order, pipeline instructions, split them into microinstructions, do aggressive branch prediction, etc. • Instruction-level parallelism enabled rapid increases in processor speeds over the last 15 years

  7. Thread-level parallelism (TLP) • This is parallelism on a more coarser scale • Server can serve each client in a separate thread (Web server, database server) • A computer game can do AI, graphics, and physics in three separate threads • Single-core superscalar processors cannot fully exploit TLP • Multi-core architectures are the next step in processor evolution: explicitly exploiting TLP

  8. What applications benefit from multi-core? • Database servers • Web servers (Web commerce) • Compilers • Multimedia applications • Scientific applications, CAD/CAM • In general, applications with Thread-level parallelism(as opposed to instruction-level parallelism)

  9. L1 D-Cache D-TLB Integer Floating Point Schedulers Uop queues L2 Cache and Control Rename/Alloc BTB Trace Cache uCode ROM Decoder Bus BTB and I-TLB A technique complementary to multi-core:Simultaneous multithreading • Problem addressed:The processor pipeline can get stalled: • Waiting for the result of a long floating point (or integer) operation • Waiting for data to arrive from memory • Other execution unitswait unused

  10. Simultaneous multithreading (SMT) • Permits multiple independent threads to execute SIMULTANEOUSLY on the SAME core • Weaving together multiple “threads” on the same core • Example: if one thread is waiting for a floating point operation to complete, another thread can use the integer units

  11. Without SMT, only a single thread can run at any given time L1 D-Cache D-TLB Integer Floating Point Schedulers Uop queues L2 Cache and Control Rename/Alloc BTB Trace Cache uCode ROM Decoder Bus BTB and I-TLB Thread 1: floating point

  12. Without SMT, only a single thread can run at any given time L1 D-Cache D-TLB Integer Floating Point Schedulers Uop queues L2 Cache and Control Rename/Alloc BTB Trace Cache uCode ROM Decoder Bus BTB and I-TLB Thread 2:integer operation

  13. SMT processor: both threads can run concurrently L1 D-Cache D-TLB Integer Floating Point Schedulers Uop queues L2 Cache and Control Rename/Alloc BTB Trace Cache uCode ROM Decoder Bus BTB and I-TLB Thread 2:integer operation Thread 1: floating point

  14. SMT not a “true” parallel processor • Enables better threading (e.g. up to 30%) • OS and applications perceive each simultaneous thread as a separate “virtual processor” • The chip has only a single copy of each resource • Compare to multi-core:each core has its own copy of resources

  15. Multi-core: threads can run on separate cores L1 D-Cache D-TLB L1 D-Cache D-TLB Integer Floating Point Integer Floating Point Schedulers Schedulers L2 Cache and Control Uop queues Uop queues L2 Cache and Control Rename/Alloc Rename/Alloc BTB Trace Cache uCode ROM BTB Trace Cache uCode ROM Decoder Decoder Bus Bus BTB and I-TLB BTB and I-TLB

  16. Multi-core: threads can run on separate cores L1 D-Cache D-TLB L1 D-Cache D-TLB Integer Floating Point Integer Floating Point Schedulers Schedulers L2 Cache and Control Uop queues Uop queues L2 Cache and Control Rename/Alloc Rename/Alloc BTB Trace Cache uCode ROM BTB Trace Cache uCode ROM Decoder Decoder Bus Bus BTB and I-TLB BTB and I-TLB

  17. Combining Multi-core and SMT • Cores can be SMT-enabled (or not) • The different combinations: • Single-core, non-SMT: standard uniprocessor • Single-core, with SMT • Multi-core, non-SMT • Multi-core, with SMT • The number of SMT threads:2, 4, or sometimes 8 simultaneous threads • Intel calls them “Hyper-Threads” (HT Technology)

  18. SMT Dual-core: all four threads can run concurrently L1 D-Cache D-TLB L1 D-Cache D-TLB Integer Floating Point Integer Floating Point Schedulers Schedulers L2 Cache and Control Uop queues Uop queues L2 Cache and Control Rename/Alloc Rename/Alloc BTB Trace Cache uCode ROM BTB Trace Cache uCode ROM Decoder Decoder Bus Bus BTB and I-TLB BTB and I-TLB

  19. Comparison: multi-core vs SMT • Multi-core: • Since there are several cores,each is smaller and not as powerful(but also easier to design and manufacture) • However, great with thread-level parallelism • SMT • Can have one large and fast superscalar core • Great performance on a single thread • Mostly still only exploits instruction-level parallelism

  20. The memory hierarchy for threading • If simultaneous multithreading only: • all caches shared • Multi-core chips: • L1 caches private • L2 caches private in some architecturesand shared in others • Memory is always shared

  21. Intel Xeon Dual-core hyper-threads • Dual-coreIntel Xeon processors • Each core is hyper-threaded • Private L1 caches • Shared L2 caches C O R E 1 C O R E 0 L1 cache L1 cache L2 cache memory

  22. Designs with private L2 caches C O R E 1 C O R E 0 C O R E 1 C O R E 0 L1 cache L1 cache L1 cache L1 cache L2 cache L2 cache L2 cache L2 cache L3 cache L3 cache memory memory Both L1 and L2 are private Examples: AMD Opteron, AMD Athlon, Intel Pentium D A design with L3 cachesExample: Intel Itanium 2

  23. Private vs shared caches • Advantages of private: • They are closer to core, so faster access • Reduces contention • Advantages of shared: • Threads on different cores can share the same cache data • More cache space available if a single (or a few) high-performance thread runs on the system

  24. The cache coherence problem • Since we have private caches:How to keep the data consistent across caches? • Each core should perceive the memory as a monolithic array, shared by all the cores MESI cache Coherence Protocol

  25. The Core i3 500 series products are dual cores and they do have hyper-threading and support virtualization, but they do not have Turbo Boost. The Core i5 600 series products are dual cores which have hyper-threading, Turbo Boost, virtualization, and the AES instruction set.

  26. TDP: Thermal Design Power

  27. The Turbo Boost Technology • When using fewer cores, transistors built into the chip disconnected from the power bus • When programs need a single thread, then the connected core is automatically pumped up with extra voltage and over clock for a short period of time until the job is done. • The Turbo Boost decodes when to do what to maximize performance

  28. The Turbo Boost Technology • Of course, consistently over clocking a machine can overheat the chip and render it useless fairly rapidly • Intel has ensured that its Mobile Nehalem parts (codenamed Clarksfield) protect themselves through self monitoring and shutting down if temperature limits are breached. (How about constantly shutting down the cores !!)