Other material Original research papers (see reference list) Uzi Vishkin, http://www.umiacs.umd.edu/~vishkin/index.shtml http://www.umiacs.umd.edu/~vishkin/index.shtml Class notes on Thinking in Parallel: Some Basic Data-Parallel Algorithms and Techniques, 2010, http://www.umiacs.umd.edu/~vishkin/PUBLICATIONS/classnotes.pdf http://www.umiacs.umd.edu/~vishkin/PUBLICATIONS/classnotes.pdf
CPU’s have been getting faster…but that stopped in mid-2000’s. Why?
Pollack FJ. New microarchitecture challenges in the coming generations of CMOS process technologies (keynote address)(abstract only). Proceedings of the 32nd annual ACM/IEEE international symposium on Microarchitecture. Haifa, Israel: IEEE Computer Society; 1999:2.
Problems can be solved in much faster times. Predictive protein binding “Meet Tanuki, a 10,000-core Supercomputer in the Cloud” Based on Amazon EC2 Cloud service, client Genentech Compute time reduced from about a month to 8 hours http://www.bio-itworld.com/news/04/25/2011/Meet-Tanuki-ten-thousand-core- supercomputer-in-cloud.html
Army: “Want computers to work like the human brain” http://www.wired.com/dangerroom/2011/04/army-wants-a-computer-that-acts-like-a-brain/
Where are we going? o NVIDIA has Fermi GPU GeForce GTX 590 with 1024-core processor (2011), programmable using CUDA, ~2500 GFLOPS. o In 2005, Intel started manufacturing dual-core CPU’s. o In 2010, Intel and AMD are manufacturing six-core CPU’s, ~11 GFLOPS (non-SSE). o In 2012, Intel will introduce Knights Corner, a 50-core processor. CPU vs GPU
The largest supercomputer is the Tianhe-IA (Nov 2010 http://www.top500.org/ ) http://www.top500.org/ 7168 Xeon X5670 6- core processors 7168 Nvidia M2050 GPU processors with 448 CUDA Cores Wikipedia.org. Tianhe-I, 2010.
One of the “seven” up and coming language [Wayner 2010]Wayner 2010 Brings parallel computing to the common man. For one GPU, a speed ups of 100 times or more over a serial CPU solution is common. Used in many different applications. Coming to mobile devices.
A task is a sequence of instructions that executes as a group. Tasks continue until halt, exit, or return.
Computers do not directly execute tasks. Computer execute Instructions, which are used to model a task.
Execution of tasks are not concurrent and not simultaneous. A sequence of tasks is called a thread. Step 1Step 3Step 2
Execution of tasks of multiple threads are concurrent but not necessarily simultaneous. Step 1Step 3Step 2 Step 1Step 3Step 2
Execution of tasks of multiple threads are concurrent and simultaneously executing on multiple machines. Goal is minimized time and work. Step 1Step 3Step 2 Step 1Step 3Step 2
Nowadays, many people use the terms interchangeably. Lin, Y. and L. Snyder (2009). Why? Since the tasks of the threads can occur in any order, so behavior is unpredicatable. Read xSet x = ySet y = x + 1 Read xSet x = ySet y = x + 2 Read xSet x = ySet y = x + 3
Basic five-stage pipeline in a RISC machine (IF = Instruction Fetch, ID = Instruction Decode, EX = Execute, MEM = Memory access, WB = Register write back). In the fourth clock cycle (the green column), the earliest instruction is in MEM stage, and the latest instruction has not yet entered the pipeline.RISC
An instruction pipeline is a technique used in the design ofcomputers and other digital electronic devices to increase their instruction throughput (the number of instructions that can be executed in a unit of time).computers Unfortunately, not all instructions are independent!
f = 1 e = 2 a = b = c = d = 3 s1. e = a + b s2. f = c + d s3. g = e * f e = a + b f = c + d g = e * f Result: g = 36
f = 1 e = 2 a = b = c = d = 3 s1. e = a + b s2. f = c + d s3. g = e * f e = a + b f = c + d g = e * f Result: g = 6
f = 1 e = 2 a = b = c = d = 3 s1. e = a + b s2. f = c + d s3. g = e * f e = a + b f = c + d g = e * f “s3 is flow dependent on s1” There are other types of dependencies.
Thread-level parallelism = task parallelism Example, recalculation of a spreadsheet
Process-level parallelism Example, two independent programs (Freecell and Email) Granularity is the size of the problem (e.g., instruction vs. thread vs. process)
TaTa TaTa TbTb TbTb TcTc TcTc TdTd TdTd TeTe TeTe TaTa TaTa TbTb TbTb TcTc TcTc TdTd TdTd TeTe TeTe What is the time of computation if b, c, d, e are tasks that can be run in parallel on four processors? Serial computation: T a … T e
Amdahl’s law TaTa TaTa TbTb TbTb TcTc TcTc TdTd TdTd TeTe TeTe TbTb TbTb TcTc TcTc TdTd TdTd TeTe TeTe TaTa TaTa Let f = fraction of time that must be serially executed
Amdahl’s law Question: If a problem is not parallelizable by even only a small fraction, throwing more processors at a problem will not help speed it up. So, why try for a parallel solution? Para dox Gustafson? (G.’s Law is equivalent to Amdahl…)
Question: If a problem is not parallelizable by even only a small fraction, throwing more processors at a problem will not help speed it up. So, why try for a parallel solution? Answer: A prerequisite to applying Amdahl’s or Gustafson’s formulation is that the serial and parallel programs take the same number of total calculation steps for the same input.
Use of a resource constrained serial execution as the base for speedup calculation; and Use a parallel implementation that can bypass large amount of calculation steps while yield the same output of the corresponding serial algorithm. Any algorithm in which the complexity of verification is faster than the complexity of the solution [Shi 1995] => most algorithms!
CPU = “Central Processing Unit” GPU = “Graphics Processing Unit” What’s the difference?
Why do we classify hardware? In order to program a parallel computer, you have to understand the hardware very well. The basic classification is Flynn taxonomy (1966): SISD, SIMD, MIMD, MISD
Single Instruction Single Data Examples: MOS Technology 6502 Motorola 68000 Intel 8086
Single Instruction Multiple Data Examples: ILLIAC IV CM-1, -2 Intel Core, Atom NVIDIA GPU’s
Multiple Instruction Single Data Examples: Space shuttle computer
Multiple Instruction Multiple Data Examples: BBN Butterfly, Cedar, CM-5, IBM RP3, Intel Cube, Ncube, NYU Ultracomputer
Parallel Random Access Machine (PRAM). Idealized SIMD parallel computing model. Unlimited RAM’s, called Processing Units (PU). RAM’s operate with same instructions and synchronously. Shared Memory unlimited, accessed in one unit time. Shared Memory access is one of CREW, CRCW, EREW. Communication between RAM’s is only through Shared Memory.
PRAM is used for specifying an algorithm and analyzing the complexity of it. PRAM-based algorithms can be adapted to SIMD architectures. PRAM algorithms can be converted into CUDA implementations relatively easily.
Parallel for loop for P i, 1 ≤ i ≤ n in parallel do … end