CSCI465/ECEN433 Parallel Computing Lecture 2 Quiz

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What is memory latency?

The measure of how fast the processor can access the cache
The time taken for data to be loaded into the processor cache
The time taken for a memory request from a processor to be serviced by the memory system (correct)
The rate at which the memory system can provide data to a processor

What happens when a processor 'stalls'?

It stops processing altogether
It cannot run the next instruction due to a dependency on a previous instruction (correct)
It skips the stalled instruction and moves to the next one
It runs faster to catch up on the stalled instructions

Why do modern processors have caches?

To increase the memory bandwidth
To reduce the number of cores in the processor
To increase the clock speed of the processor
To reduce memory access latency and reduce stalls (correct)

What does memory access time measure?

The latency involved in accessing memory (A) Signup and view all the answers

Which cache level typically has the lowest capacity but the fastest access times?

L1 cache (C) Signup and view all the answers

What is the function of caches in reducing stalls in processors?

To keep frequently accessed data closer to the processor, reducing memory access latency (C) Signup and view all the answers

What is the purpose of caches in modern CPUs?

To predict and prefetch data for faster access (A) Signup and view all the answers

How does prefetching help in reducing stalls in CPU performance?

By predicting and loading data before it is accessed (C) Signup and view all the answers

What can happen if prefetching guesses the data access pattern wrongly?

It reduces performance by hogging bandwidth (A) Signup and view all the answers

How does multi-threading help in CPU performance?

By interleaving processing of multiple threads to hide stalls (D) Signup and view all the answers

What is the main idea behind multi-threading in CPUs?

To hide stalls and improve performance (D) Signup and view all the answers

Why is multi-threading considered a latency-hiding technique?

Because it interleaves processing of multiple threads to mask stalls (C) Signup and view all the answers

What is the main benefit of multi-threading in a core's ALU?

Hides memory latency (C) Signup and view all the answers

Which of the following is a cost associated with multi-threading?

Increased memory bandwidth (D) Signup and view all the answers

How does increasing the number of threads impact cache space per thread?

Reduces cache space per thread (D) Signup and view all the answers

What is the purpose of the L2 cache in a multi-core chip?

Expand the available cache memory (D) Signup and view all the answers

Which feature distinguishes simultaneous multi-threading (SMT) from temporal multi-threading?

Core chooses instructions from multiple threads (B) Signup and view all the answers

What is a critical drawback of using simultaneous multi-threading (SMT)?

Higher storage requirement for thread contexts (B) Signup and view all the answers

What is the key idea behind throughput-oriented systems?

Increasing overall system throughput by potentially increasing time for each thread (D) Signup and view all the answers

In hardware-supported multi-threading, what does the core manage for multiple threads?

Execution contexts (D) Signup and view all the answers

What is the purpose of interleaved multi-threading in processors?

To help use ALU resources more efficiently with high-latency operations (D) Signup and view all the answers

Why does a throughput-oriented system potentially increase the time for each thread to complete work?

To increase the system's overall throughput (A) Signup and view all the answers

How does high-latency hiding ability differ between small and large execution contexts?

Small contexts have higher hiding ability (B) Signup and view all the answers

What is the main benefit of hardware-supported multi-threading for cores?

Helping use ALU resources more efficiently with high-latency operations (A) Signup and view all the answers

What is the purpose of the 'sinx' function in the given code snippet?

Performing a mathematical operation involving the input value (D) Signup and view all the answers

What is the role of the 'my_args' struct in the provided code?

To store arguments for thread functions (C) Signup and view all the answers

Which part of the code snippet is responsible for launching a new thread?

pthread_create(&thread_id, NULL, my_thread_start, &args) (C) Signup and view all the answers