Structure of Computer Systems - Course 6
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Questions and Answers

What is the main disadvantage of the write-through caching method?

  • It eliminates the need for cache invalidation mechanisms.
  • It may lead to data inconsistency during write operations.
  • It requires more memory bandwidth than write-back.
  • It incurs a high overhead due to frequent memory updates. (correct)

In a snooping and invalidation system, what action do the cores perform when they detect a write from another core?

  • They store the write to be processed later.
  • They invalidate their cache line to prevent inconsistency. (correct)
  • They ignore the write if it doesn't affect their cache.
  • They update their cache immediately to reflect the change.

Which of the following is an advantage of symmetric multi-core architectures?

  • They can perform tasks more efficiently than asymmetric cores.
  • They simplify the development and execution of multithreaded programs. (correct)
  • They offer greater performance for single-threaded applications.
  • They use different cores for different tasks to maximize efficiency.

What type of architecture involves cores that are interchangeable and can perform any tasks?

<p>Symmetric architecture (A)</p> Signup and view all the answers

What potential issue can arise from the write-back caching method?

<p>Extended periods of data inconsistency. (C)</p> Signup and view all the answers

Which type of processor architecture has cores that share the same structure and functionality?

<p>Symmetric cores (B)</p> Signup and view all the answers

What is the disadvantage of using shared cache in multi-core processors?

<p>Conflict between cores in space allocation (D)</p> Signup and view all the answers

Which memory access type allows cores to have varying access speeds based on their location?

<p>Non-uniform memory access (C)</p> Signup and view all the answers

In a multi-core processor with crossbar connection, what is the role of the switch?

<p>To facilitate multiple connections (A)</p> Signup and view all the answers

Which of the following statements is true regarding the advantages of shared cache?

<p>One core can pre-fetch data for other cores. (B)</p> Signup and view all the answers

What defines heterogeneous multi-core processors?

<p>Cores designed for multiple types of tasks (D)</p> Signup and view all the answers

What is a potential drawback of a shared cache in multi-core processors?

<p>Increased latency time due to switching (D)</p> Signup and view all the answers

Which type of multi-core architecture allows different caches per core while maintaining a shared main memory?

<p>Symmetric multi-core (B)</p> Signup and view all the answers

What does cache coherence in processors primarily address?

<p>How to keep data consistent across caches (C)</p> Signup and view all the answers

Which type of memory access typically allows for faster access for cores located closer together?

<p>Non-uniform memory access (NUMA) (D)</p> Signup and view all the answers

What does data level parallelism (DLP) primarily operate on?

<p>Identical operations on a dataset (A)</p> Signup and view all the answers

What is an important aspect of thread level parallelism (TLP) that can pose execution issues?

<p>Data consistency (B)</p> Signup and view all the answers

Amdahl's law helps to determine what in parallel processing?

<p>The potential speedup of a parallel execution (B)</p> Signup and view all the answers

What purpose do buffers serve in hyper-threading?

<p>To hold intermediate results of two threads (D)</p> Signup and view all the answers

What factor does 'n' represent in Amdahl's law?

<p>Number of nodes or threads (B)</p> Signup and view all the answers

What is a key advantage of hyper-threading?

<p>Enables execution of threads during stalls (A)</p> Signup and view all the answers

What is a significant reason for the development of multi-core processors?

<p>Increasing power consumption and dissipation problems (C)</p> Signup and view all the answers

In the context of parallel execution, what does the term 'synchronization' refer to?

<p>The coordination of concurrent threads (D)</p> Signup and view all the answers

How does thread level parallelism (TLP) improve computer processing?

<p>By enabling concurrent execution of instruction streams (B)</p> Signup and view all the answers

Which of the following describes 'distributed computing facilities'?

<p>Multiple CPUs on different computers connected through a network (D)</p> Signup and view all the answers

What is a characteristic of cloud architectures?

<p>They offer computing resources dynamically as a service (C)</p> Signup and view all the answers

Which type of implementation consists of multiple CPUs in a single integrated circuit?

<p>Multi-core architectures (C)</p> Signup and view all the answers

What issue is associated with designing very complex CPUs?

<p>Requires extensive coordination among large design teams (B)</p> Signup and view all the answers

What is one of the limits faced by pipeline architectures?

<p>Achieved maximum efficiency lies around 20 pipeline stages (C)</p> Signup and view all the answers

Which statement is true regarding multi-core systems?

<p>Multi-core processors can handle multiple tasks simultaneously (D)</p> Signup and view all the answers

What signifies a 'hyper-threaded' system?

<p>It utilizes a single core to handle multiple threads (B)</p> Signup and view all the answers

Which of the following characteristics define asymmetric (heterogeneous) architecture in multi-core processors?

<p>Integrating a main core with multiple specialized cores (A)</p> Signup and view all the answers

What is one primary advantage of multi-core processors?

<p>Shorter signal travel distances leading to less degradation (A)</p> Signup and view all the answers

In the IBM cell architecture, what is the role of the Power Processor Element (PPE)?

<p>Coordinating and managing data transfers (C)</p> Signup and view all the answers

Which of the following statements about the performance of multi-core processors is true?

<p>Single-core processors can outperform multi-core processors in some cases. (B)</p> Signup and view all the answers

What is a disadvantage typically associated with multi-core processors?

<p>They can struggle with memory bandwidth limitations. (C)</p> Signup and view all the answers

How does cache coherency impact the performance of multi-core processors?

<p>It allows for much higher clock rates, improving performance. (C)</p> Signup and view all the answers

What type of cores does the IBM cell processor primarily integrate?

<p>Unique, specialized cores such as graphic and multimedia cores (C)</p> Signup and view all the answers

Which factor can limit the performance advantage of dual-core processors compared to single-core processors?

<p>Shared system bus and memory bandwidth (B)</p> Signup and view all the answers

Flashcards

Data Level Parallelism (DLP)

Exploiting parallelism by executing the same operations on multiple data elements simultaneously. Think of it as applying the same instruction to a group of data at once.

Instruction Level Parallelism (ILP)

Exploiting parallelism by breaking down instructions into smaller stages and executing them concurrently. Think of it as an assembly line for instructions.

Thread Level Parallelism (TLP)

Exploiting parallelism by running multiple independent sequences of instructions, or threads, concurrently on different processors or cores.

Amdahl's Law

A mathematical model that helps estimate the maximum speedup achievable by parallelizing a program.

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Hyper-threading

A technique that allows a single processor to execute multiple threads concurrently by sharing resources and switching between them. Think of it as multitasking on a single CPU.

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Multiprocessing

A form of thread level parallelism where multiple processors or cores work together to execute a program. Think of it as distributing tasks across multiple computers.

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Synchronization between threads

The process of coordinating the execution of multiple threads to ensure they access shared resources correctly and avoid conflicting operations.

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Data consistency

Ensuring that data is consistent across all threads, preventing conflicts and maintaining data integrity when multiple threads access shared data.

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Multithreading

A method of executing a program by dividing it into smaller parts (threads) that run concurrently on multiple CPUs. Threads can be executed on different CPUs within the same physical computer (multi-core) or on different computers connected by a network (distributed computing).

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Multi-core Processor

A processor with multiple independent processing units (cores) that execute instructions concurrently. It allows for increased performance by dividing tasks among the cores.

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Distributed Computing

A parallel processing system that utilizes CPUs located in different computers connected through a network. It allows for high-performance computing by combining the resources of many machines.

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Cloud Architectures

A type of cloud computing where services are offered on demand, including computing resources (CPU and memory) and storage. Users can access these resources dynamically based on their requirements.

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Homogeneous vs. Heterogeneous

A concept in multiprocessing that differentiates between CPUs with the same or different functionalities. Homogeneous systems have CPUs with identical capabilities, while heterogeneous systems have CPUs with different specializations.

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GRID Architectures

A specific kind of distributed computing architecture often used for large-scale scientific workloads. It allows researchers and scientists to share computing resources across geographically distant institutions.

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Clock Speed Saturation

The increasing difficulty and limitations in improving the clock speed of single-core processors due to factors such as power consumption, heat dissipation, and design complexities.

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Pipeline Architectures (Instruction Level Parallelism)

A parallel processing technique within CPUs where instructions are divided into smaller parts (pipeline stages) and executed concurrently to improve performance. However, there are efficiency limitations as the pipeline becomes too complex.

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Snooping & Invalidation

A memory optimization where each core monitors the bus, and if a write from another core affects its data, the core invalidates its cache line. This prevents inconsistencies between cores' caches and the main memory.

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Symmetric Multi-core Architecture

A multi-core architecture where all cores have the same abilities and can execute any task. It's like having identical processors working together.

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Write-through

A method of handling data consistency between cores where a write operation to the cache is also written to memory. This is slower but ensures consistency.

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Asymmetric Multi-core Architecture

A multi-core architecture where cores may have different capabilities or be designed for specific purposes. It's like having a team with specialized players.

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Write-back

A memory optimization where a write operation to the cache is only written back to the main memory when the cache line is discharged. This is faster but can lead to inconsistencies.

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Symmetric Multi-Core Processor (SMP)

Each core in an SMP system has the same structure and functionality.

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Asymmetric Multi-Core Processor (ASMP)

ASMP systems have specialized cores, like coordination cores and simpler cores, with different functions.

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Symmetric Memory Access (SYMA)

SYMA refers to a multi-core system where all cores have equal access to memory.

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Non-Uniform Memory Access (NUMA)

NUMA refers to a system where different cores have different access speeds to memory depending on its location.

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Common Bus

A common bus is a shared pathway for data transfer between cores and other components (like memory).

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Crossbar

A crossbar uses a switch to allow multiple connections between cores and other components.

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Shared Cache

Shared cache is high-speed memory that multiple cores can access.

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Private Cache

Private cache is a smaller, dedicated cache that each individual core has, storing frequently used data.

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Cache Coherence

Cache coherence is a mechanism ensuring data consistency across multiple caches when they store the same data.

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Cache Coherence Protocols

Cache coherence protocols ensure that data is always consistent across multiple caches, even when it is shared between multiple cores.

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Asymmetric (Heterogeneous) Architecture

A type of multi-core processor architecture where cores are different and have specialized roles.

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Specialized Cores

A processor with a main core and multiple specialized cores for tasks like graphics, floating-point operations, and multimedia.

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IBM Cell Processor

A processor architecture that utilizes different cores with varying functionalities to improve performance and efficiency.

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Core-Aware Compilation

The process of optimizing program code to take advantage of different core functionalities to achieve the best performance.

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Reduced Signal Degradation in Multi-core Processors

The increased speed of signal transmission between cores in a multi-core processor due to shorter distances.

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Faster Cache Coherency

The capability of a multi-core processor to execute multiple instructions efficiently due to shorter signal paths and faster processing times.

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Multi-threading Application Dependency

The ability of a multi-core processor to improve application performance depends on how well the software utilizes multiple threads.

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Study Notes

Structure of Computer Systems - Course 6

  • Multi-core systems are a key topic in computer architecture.

Mutithreading and Multiprocessing

  • Exploiting different forms of parallelism:

    • Data Level Parallelism (DLP): SIMD architectures employing the same operations on a dataset.
    • Instruction Level Parallelism (ILP): Executing multiple instructions concurrently in pipelined architectures.
    • Thread Level Parallelism (TLP): Parallel execution of instruction sequences in hyper-threading, multiprocessor, GRID, cloud, and parallel computing architectures.

  • Thread Level Parallelism Execution Issues:

    • Synchronization between threads
    • Data consistency
    • Concurrent access to shared resources
    • Communication between threads

Multiprocessing

  • Amdahl's Law: Limits of performance increase in parallel execution.
    • S = speedup of a parallel execution: ts/(1-q)ts + (qts/n) Where,
  • ts* = time for sequential execution
  • tp* = time for parallel execution
  • q* = fraction of a program that can be parallelized.
  • n* = number of nodes/threads.
    • Examples illustrating Amdahl's Law with different values of q (e.g., q=50%, 75%, 95%).

Hyper-threading

  • Hyper-threading: Parallel execution of instruction streams on a single CPU.
  • Solution: To exploit potential when one thread is stalled due to hazards, another thread can be executed. Two threads executed concurrently on the same pipelined CPU. Registers used to store partial results.
  • Speedup: Approximately 30% more performance, the OS detects these as multiple logical CPUs.

Multiprocessors

  • Parallel Execution: Executing instruction streams concurrently on multiple CPUs.
  • Implementations:
    • Multi-core architectures: Multiple CPUs on one integrated circuit (IC)
    • Parallel computers: Multiple CPUs on different ICs, within the same computer infrastructure.
    • Distributed computing facilities: Multiple CPUs on different computers, networked together.
    • Networks of personal computers (PCs): Grid architectures, often used for distributed computing, especially batch processing tasks.
    • Cloud architectures: Computing resources (execution and storage) as a service. Dynamically allocated resources. Multi-core parallelism on parallel computers used to build distributed computer facilities.

Multi-core Processors

  • Why multi-core?:
    • Difficulty in increasing single-core clock speeds.
    • Power consumption and dissipation problems at higher frequencies.
    • Pipeline architectures and efficiency limits.
    • Complex CPU design and large design teams.
    • Increasingly common multi-threaded applications (servers, games, simulation).

Multi-core Processors - Issues

  • CPU Functionality: Homogeneous CPUs (same functionality) vs. heterogeneous CPUs (different functionalities)
  • Symmetric Cores (SMP): Every core has the same structure and functionality.
  • Asymmetric Cores (ASMP): Cores with differing functionalities, some cores specializing in coordination or specific operations.
  • Memory Access: Symmetric or non-uniform memory access (NUMA).
  • Connection between Cores: Common bus, crossbar, or network-on-chip.

Multi-core Processors - Architectural Solutions

  • Different designs of multi-core architectures exist to solve various problems and achieve best performance. Symmetric vs. Asymmetric designs with the use of caches and the connection between different cores.

Multi-core Processors - Shared Cache

  • Advantages: Efficient allocation, pre-fetching data, lack of cache coherence problems, less accesses to external memory.

Multi-core Processors - Cache Coherence

  • Solutions: Write-through and Write-back strategies, snooping, and invalidation protocols (Pentium Pro's P6 bus for example) to ensure data consistency across multiple caches.

Multi-core Processors - Symmetric vs Asymmetric Cores

  • Symmetric Cores: Identical cores, interchangeable roles. Easy to build and program for multi-threaded applications; examples: Intel, AMD (Dual/Quad-core, Core2) and SUN (UltraSparc T1 - Niagara).

  • Asymmetric Cores: Different core types, some cores being masters, others slaves/specialized. Better for varied functional operations. Examples: IBM Cell processor.

Multi-core Processors - Asymmetric Architecture (IBM Cell)

  • Specialized Cores (SPE): Synergistic Processing Units for specialized mathematical operations. Power Processor Element (PPE). Data transfer Coordination functions.

Multi-core Processors - Advantages

  • Reduced signal distances and degradation. Increased data rate sent in a given time period. Improved cache coherence circuitry operation. Lower power consumption for dual-core vs. two single-core processors.

Multi-core Processors - Disadvantages

  • Application performance depends on effective use of multiple threads. Single-core might outperform dual/multi in some cases. Shared CPU bus and memory bandwidth limit the advantage. Performance gains are not guaranteed for all applications.

Multi-core Processors - Thread Affinity

  • Thread Affinity: Ability to specify the core a thread runs on. This is sometimes advantageous with real-time or applications which are vulnerable to load changes on any single core. This is often managed by the operating system (soft affinity). The programmer can also set this explicitly using hard affinity.

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This quiz explores key concepts in multi-core systems, focusing on various forms of parallelism including Data Level, Instruction Level, and Thread Level Parallelism. It also discusses execution issues such as synchronization, data consistency, and Amdahl's Law. Test your understanding of these critical aspects of computer architecture.

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