Definition
Parallel processing is a computing technique in which multiple processors work together simultaneously to solve a computational problem. It involves breaking down a large problem into smaller tasks that can be processed independently and whose results are combined at the end.
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History
The concept of parallel processing dates back to the 1960s when supercomputers with multiple processors were first developed. As the cost of processors decreased over time, parallel processing expanded from supercomputing into mainstream computing. Today multi-core processors that support parallel processing are standard even in consumer devices like laptops and smartphones.
Benefits
Parallel processing offers significant benefits over sequential processing on a single processor:
- Speed: By using multiple CPUs, parallel processing can significantly reduce processing time for large computations. Many tasks can be sped up by orders of magnitude.
- Efficiency: Parallel algorithms can maximize utilization of available computing resources.
- Scalability: Parallel systems can easily be expanded by adding more processors.
Challenges
Effective parallel processing also comes with some key challenges:
- Synchronization: Ensuring threads have access to shared data without conflicts.
- Communication: Enabling communication between threads to share intermediate results.
- Load Balancing: Distributing work evenly across processors.
- Task Partitioning: Breaking up the problem to minimize dependencies.
Types of Parallel Processing
There are several types of parallel processing, categorized by how the work is distributed:
Data Parallelism
The same computation is performed across multiple processors on different subsets of the input data. Common in scientific simulations.
Task Parallelism
Different computations of the same larger problem are distributed to multiple processors. Useful for complex workflows.
Pipelining
Different stages of a sequential process are assigned to different processors analogous to an assembly line. Maximizes throughput.
Instruction-Level Parallelism
Parallelism is exploited at the CPU instruction level, e.g. through superscalar or VLIW architectures.
How Parallel Processing Works
Executing programs in parallel requires both specialized hardware and software:
Parallel Hardware
Various architectures exist for connecting multiple processors, such as shared memory machines or computer clusters. Specialized parallel processors like GPUs and hardware accelerators are also used.
Parallel Software and Algorithms
Software frameworks help developers implement parallel programs by handling underlying communication and synchronization:
Threading
Lightweight processes called threads represent tasks for available CPUs.
Message Passing
Threads running on different processors pass data through messages.
Divide and Conquer
Recursively break down problem into smaller independent sub-problems.
MapReduce
Big data processing model that splits computation across clusters.
Synchronization
Synchronization mechanisms like locks and barriers coordinate access to shared data to prevent race conditions.
Load Balancing
Strategies evenly distribute computational load across processors to maximize utilization. Work stealing algorithms dynamically shift load from overloaded to idle processors.
Parallel Processing Architectures
There are three main hardware architectures for connecting processors:
Shared Memory Architecture
All processors access a common central memory. Simplifies communication but limits scalability.
Distributed Memory Architecture
Nodes have their own private local memory and pass messages to communicate. More scalable but complex to program.
Hybrid Architecture
Combines both shared and distributed memory for the benefits of simplicity and scalability. Used in most supercomputers today.
Applications of Parallel Processing
Parallel processing unlocks performance improvements across a diverse range of computing applications:
Scientific Computing
Complex simulations of phenomena like weather, aerodynamics, nuclear reactions etc.
Artificial Intelligence
Training deep neural networks leverages massive parallelism of GPUs.
Computer Graphics
Rendering
Ray tracing and rasterization of high resolution images and video.
Animation
Near real-time rendering of CGI for films and video games.
Data Mining
Finding insights in huge datasets using Map reduce on compute clusters.
Financial Modeling
Valuation of complex derivatives and portfolios uses Monte Carlo simulation.
Future of Parallel Processing
Ongoing hardware and software advances will further expand parallel processing:
Quantum Computing
Quantum bits allow massive intrinsic parallelism by representing all combinations of inputs simultaneously.
Optical Computing
Photons have intrinsic parallelism and higher speeds than electrons in traditional hardware.
DNA Computing
Molecular reactions have massive inherent parallelism but is still an emerging approach.
More Cores and Accelerators
Chipmakers are cramming more cores optimized for parallelism onto each chip while accelerators handle specific tasks even faster in parallel.
Parallel processing underpins modern computing and will only grow more prevalent as multi-core processors and specialized hardware accelerators become standard across all types of computers big and small. Clever parallel algorithms and software frameworks that simplify parallel development will enable users to take full advantage of parallel hardware for a broad range of cutting edge applications.
FAQs
What are the limitations of parallel processing?
The main limitations are synchronizing shared access between processors, evenly distributing workloads, and partitioning tasks to minimize dependencies. Parallel performance also reaches diminishing returns as these overheads dominate with too many processors.
How is parallel processing different from concurrent processing?
Parallel processing focuses on computation speedup by using multiple CPUs simultaneously while concurrency provides responsiveness by allowing multiple tasks to make progress regardless of speed.
What programming languages are best for parallel processing?
Languages like C/C++, Rust, Go, and Java have good concurrency support. Frameworks like OpenMP, MPI, CUDA help parallelize programs. Some functional languages have parallelism built-in.
Why can’t all algorithms be parallelized efficiently?
Many algorithms have intrinsic dependencies that limit exploitable parallelism no matter how they are partitioned across processors. These sequential portions bottleneck overall performance.
What companies are leaders in parallel processing?
Major companies advancing parallel processing include Intel, Nvidia, AMD, IBM, Oracle, Microsoft through hardware, cloud computing services, frameworks and tools. National laboratories like Oak Ridge, Argonne and Lawrence Livermore are key for supercomputing.
