L18iMulti - CS324: Computer Architecture CS324: Computer...

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S324: Computer Architecture CS324: Computer Architecture Lecture 18: Multicores & Multiprocessors
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Improving Performance ± Pipelining ± Instruction Level Parallelism (ILP) Out-of-order (uses register renaming) Deeper pipeline: more stages -> more instructions executing in parallel Multiple issue: multiple instructions issued per cycle. ± 3-6 per cycle typical. ± Determined statically (compile time) or dynamically (runtime) ± e.g. Superscalar dd more functional units or pipelines to CPU Add more functional units or pipelines to CPU
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Definitions: threads vs processes ± Process : a “program” with its own address space. – A process has at least one thread! ± thread of execution: independent sequential computational task w/own control flow tack Stack – registers, etc. – An easy way to describe/think about parallelism • A program can split, or fork itself into separate threads, which can (in theory) execute simultaneously. • Same process can have many threads sharing same virtual address space • Switching threads faster than switching processes! h d0 CPU Time Thread0 Thread1 Thread2
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ultithreading ± Multithreading – Single processor:The operating system schedules threads and processes by moving them between states (running, ready, wait, etc) – Mulitprocessor or multicore: concurrent execution with each processor or core runs a particular thread ± ILP requires more hardware -> more power! – We’re nearing the limit with respect to number of transistors we can afford to run ± Shift toward multi-processing
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New Parallelism? What’s different this me? time? “ his shift toward increasing parallelism is not a triumphant This shift toward increasing parallelism is not a triumphant stride forward based on breakthroughs in novel software and architectures for parallelism; instead, this plunge into parallelism is actually a retreat from even greater challenges that thwart efficient silicon implementation of traditional uniprocessor architectures.” p – Berkeley View, December 2006 ± HW/SW Industry bet its future that breakthroughs will appear before it’s too late view.eecs.berkeley.edu
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Introduction ± Goal: connecting multiple computers to get higher erformance performance – Multiprocessors – availability, power efficiency, scalability ± Job-level (process-level) parallelism – High throughput for independent jobs ± Parallel processing program – Single program run on multiple processors ulticore microprocessors ± Multicore microprocessors – Chips with multiple processors (cores)
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ardware and Software Hardware and Software ± Hardware – Serial: e.g., Pentium 4 – Parallel: e.g., quad-core Xeon e5345 ± Software – Sequential: e.g., matrix multiplication – Concurrent: e.g., operating system ± Sequential/concurrent software can run on serial/parallel hardware – Challenge: making effective use of parallel hardware
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arallel Programming Challenges Parallel Programming Challenges eed to get significant performance improvement ±
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L18iMulti - CS324: Computer Architecture CS324: Computer...

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