Lecture 29 : MEMORY HIERARCHY DESIGN (PART 2)

Summary

The script discusses the intricacies of memory, particularly focusing on cache memory. It explores the speed gains from using cache and how it fits into Amdahl's Law. The lecture delves into accessing data and instructions efficiently, touching on the constraints of memory hierarchy and the significance of cache hit rates. It also examines the performance impact of different cache configurations, such as L1 and M1/M2 caches, and the concept of block addressing. The discussion concludes with the importance of optimizing memory access for high-performance computing, setting the stage for further exploration in the next lecture.

Takeaways

• 😀 The lecture discusses memory in detail, particularly focusing on cache memory.
• 💡 Cache usage can significantly increase speed, as demonstrated by the formula involving 'r' and 'H', resulting in a 4x speed gain.
• 📚 Amdahl's Law is introduced to explain the limits of improving performance by optimizing code.
• 🔍 The lecture emphasizes the importance of accessing data and instructions quickly, which is facilitated by lower latency memory.
• 📉 The script outlines the concept of miss penalties and how they are calculated, affecting the overall access time.
• 💻 It explains the difference between accessing data in cache versus main memory, highlighting the efficiency of cache.
• 🔑 The concept of multi-level caches is introduced, where L1 cache is faster but has a smaller capacity compared to L2 cache.
• 🧩 The lecture touches on the idea of block size in cache, which is crucial for efficient data access.
• 🛠️ It discusses the importance of block mapping in cache, which is essential for processor performance.
• 💾 The script concludes by discussing the impact of memory hierarchy on overall system performance, leading into the next lecture.

Q & A

What is the main topic discussed in the lecture?

The main topic discussed in the lecture is memory, specifically focusing on cache memory and its efficiency.

What is the significance of the numbers r and H in the context of cache memory?

In the context of cache memory, r represents the number of blocks in the cache, and H is the hit ratio, which indicates the efficiency of the cache in retrieving data.

What does the formula used in the lecture to calculate the speed of cache memory imply?

The formula used implies that the speed of cache memory is directly related to the hit ratio (H) and the number of blocks (r), resulting in a speed of 4 in this example, which is then compared to Amdahl's law.

What is Amdahl's law and how does it relate to the discussion in the lecture?

Amdahl's law is a principle that predicts the theoretical maximum speedup of a system when a part of it is improved. In the lecture, it is used to discuss the limitations of speed improvements when only the cache memory is optimized.

What is the purpose of providing lower constraints in the context of data and instructions access?

Lower constraints are provided to ensure that data and instructions can be accessed efficiently within a single cycle, which is beneficial for the overall performance of the system.

What does the term 'M1' signify in the script?

M1 signifies the first level of cache memory hierarchy, which is typically the fastest and closest to the processor.

How does the concept of 'average access time' relate to the efficiency of cache memory?

The average access time is a measure of how quickly data can be retrieved from the cache memory. A lower average access time indicates higher efficiency and faster data retrieval.

What is the significance of the term 'memory hierarchy' in the lecture?

The term 'memory hierarchy' refers to the multi-level structure of memory in a computer system, where different levels of memory (like cache, RAM, etc.) are used to optimize speed and capacity.

Why is it important to consider the size of a block when discussing cache memory?

The size of a block in cache memory is important because it affects the efficiency of data storage and retrieval. Smaller blocks can lead to more efficient use of cache space, while larger blocks can reduce the overhead of managing many small blocks.

What is the role of the main memory in the context of the memory hierarchy discussed in the lecture?

The main memory, or RAM, serves as the primary storage for a computer system and is accessed when data is not found in the cache memory levels. It is slower compared to cache memory but has a larger capacity.

How does the concept of 'virtual memory' relate to the discussion on memory hierarchy?

Virtual memory is a memory management technique that extends the available memory by using disk space as an extension of RAM. It is not directly discussed in the lecture but is part of the broader memory management strategies that complement cache memory.

Outlines

00:00

💾 Introduction to Memory

The script begins with a welcome to the upcoming lecture on memory, specifically focusing on the example of cache memory. It discusses the potential for cache memory to enhance speed and introduces variables r and H to calculate the speed gained from using cache. The formula used is simplified to yield a speed of 4, which is then compared to Amdahl's law. The lecture suggests that for real-time data and signal processing, the speed gained is beneficial, and there are certain constraints like Miss 1, which is a circle, indicating the information is processed and the average access time is discussed.

05:04

🔍 Understanding Memory Access

This paragraph delves into how memory access can be discovered and the overall memory is not found. It emphasizes that data is generated and the average access time is demonstrated as being reduced. The example provided shows the efficiency of two different caches, highlighting that in practice, there are more than two levels of cache, but the discussion is simplified to two levels, M1 and M2. The concept is expanded to consider what happens with multiple levels, suggesting that the approach for two levels can be extended to many. The paragraph concludes with a focus on how to calculate the hit ratio in memory and the absence of access time, which is managed through data.

10:21

📚 Analyzing High-Level Memory

The discussion shifts to analyzing high-level memory, specifically the L1 cache. It mentions that there are no specific algorithms or explorations that can be done quickly, but if a hit is achieved, it can be processed in a timely manner. The concept of blocking between levels is introduced, where some questions arise about the nature of a block. The paragraph suggests that processors are obtained again, indicating a continuation of the exploration into memory structures.

15:33

🛠️ Block Identification and Memory Access

This section highlights the importance of block identification in memory. It explains that blocks are identified, then accessed, and the size of these blocks is small, leading to a limited number of blocks being called at one time. The writing mechanism refers to what happens in the cache when the writing operation is managed. The paragraph discusses the strategies needed for this specific operation, emphasizing the importance of computers in this particular category and then shifting the focus to activating the main memory area.

20:49

🌐 Fundamentals of Virtual Memory

The script touches on the fundamentals of virtual memory, noting that it is not detailed in the Intel Core i7 processor. It mentions the next generation, such as the Core-i7 Sandy Bridge controller, and how the lecture will conclude with an analysis of how memory performance impacts the overall system, which was observed in the previous discussions.

26:33

📖 Conclusion of the Lecture

The final paragraph concludes the lecture with a simple thank you, summarizing the overall discussion on memory and its performance in the system.

Keywords

💡Memory

Memory in computing refers to the digital storage that allows information to be stored and accessed by a computer. In the context of the video, memory is central to the discussion of computer architecture and performance. The script mentions various types of memory, including cache memory, which is used to speed up data access. The video explores how memory hierarchy and access times impact overall system performance.

💡Cache

A cache in computer science is a high-speed data storage layer that is closer to the processor than the main memory. It is used to reduce the average time to access data from the main memory. The script discusses cache memory and its role in improving the speed of data retrieval, which is crucial for the efficiency of a computer system.

💡Hit Ratio

The hit ratio in cache memory refers to the percentage of times that data is found in the cache when requested. A high hit ratio means that the cache is effective at storing frequently accessed data, reducing the need to access slower main memory. The script mentions calculating the hit ratio, which is essential for evaluating the performance of cache memory.

💡Miss Penalty

Miss penalty in the context of cache memory is the additional time it takes to fetch data from the main memory when it is not found in the cache. The script discusses the concept of miss penalty, which is a critical factor in understanding the efficiency of cache memory and the overall performance of a computer system.

💡Access Time

Access time refers to the time it takes to read or write data from or to a memory location. The video script mentions average access time, which is a measure of the efficiency of memory systems. Lower access times are desirable as they contribute to faster data retrieval and overall system performance.

💡Memory Hierarchy

Memory hierarchy in computer architecture is a multi-level data storage system that ranges from high-speed, low-capacity memory (like cache) to low-speed, high-capacity memory (like hard drives). The script discusses the concept of memory hierarchy and how it is structured to optimize data access speeds and system performance.

💡Block

In the context of the script, a block refers to a unit of data that is transferred between different levels of the memory hierarchy. The script mentions blocks in the context of cache memory, where data is organized into blocks to optimize the efficiency of data storage and retrieval.

💡Miss Rate

Miss rate in cache memory is the probability that a requested data item is not in the cache. The script discusses calculating the miss rate, which is an important metric for understanding the effectiveness of a cache memory system.

💡Memory Access

Memory access refers to the process of reading or writing data to a memory location. The video script talks about the average memory access time and how it is affected by the efficiency of the cache memory system, which is a key factor in the overall performance of a computer.

💡Data Prefetching

Data prefetching is a technique used to improve the performance of a computer system by loading data into cache memory before it is needed. The script mentions prefetching as a strategy to reduce the latency of memory access, which can enhance the speed of data retrieval.

💡Instruction

In computing, an instruction is a command that a processor can execute. The script refers to instructions in the context of accessing data and how the processor handles memory access requests. Efficient instruction handling is crucial for the performance of a computer system.

Highlights

Welcome to the lecture on memory.

Discussion on cache memory and its benefits.

Calculation of speed gain using cache memory with example values for r and H.

Introduction to Amdahl's Law and its significance in computing.

Importance of accessing data and instructions efficiently within a single cycle.

Explanation of constraints such as Miss 1 cycle and its impact.

Understanding how to calculate average access time and its implications.

Concept of memory hierarchy and its role in data processing.

Analysis of cache efficiency and performance metrics.

Differentiating between two types of cache and their respective performance.

Exploration of multi-level hierarchy in memory systems.

Discussion on how to expand the concept of two levels to multiple levels in memory hierarchy.

Practical example of memory system as a testbed for experimental memory.

Methodology for measuring access time in memory systems.

Impact of memory hierarchy on CPU performance and how it differs from memory.

Role of higher-level memory in processing requests and its efficiency.

Introduction to L1 cache and its significance in memory performance.

Discussion on the concept of blocking and its importance in processor design.

Importance of block identification and access in memory systems.

Analysis of the size of blocks and its effect on memory access.

Explanation of the writing process and the tactics used in executing operations.

Identification of the specific computer used for optimization in this context.

Conclusion of the lecture with a summary of the impact of memory architecture on performance.

Transcripts

ಮುಂದಿನ ಉಪನ್ಯಾಸ 29ಕ್ಕೆ ಸುಸ್ವಾಗತ.

ಇಲ್ಲಿ ನಾವು ಮೆಮೊರಿ ಬಗ್ಗೆ ವಿವರವಾಗಿ ಚರ್ಚಿಸುತ್ತೇವೆ.

ಈ ಉದಾಹರಣೆಯನ್ನು ಇಲ್ಲಿ ತೆಗೆದುಕೊಳ್ಳೋಣ.

ಕ್ಯಾಶ್ ಮೆಮೊರಿ ಯನ್ನು ಸಹ ಹೊಂದಬಹುದು.

ಕ್ಯಾಶ್ ಅನ್ನು ಬಳಸುವುದರಿಂದ ನಾವು ಎಷ್ಟು ವೇಗವನ್ನು

ಪಡೆಯುತ್ತೇವೆ?

ಆದ್ದರಿಂದ, ಇಲ್ಲಿ r 6 ಆಗಿರುತ್ತದೆ ಮತ್ತು

H 0.90 ಆಗಿರುತ್ತದೆ.

ಆದ್ದರಿಂದ, ನಾವು ಸರಳವಾಗಿ ಈ ಸೂತ್ರವನ್ನು ಹಾಕುತ್ತೇವೆ

ಮತ್ತು ನಾವು 4 ಅನ್ನು ಪಡೆಯುತ್ತೇವೆ.

ಆದ್ದರಿಂದ, ನಾವು 4 ರ ವೇಗವನ್ನು ಪಡೆಯುತ್ತೇವೆ.

ಇದು ಅಮದಾಲ್‌ನ ಕಾನೂನಿದಲ್ಲಿ ಇರಿಸಲಾಗುತ್ತದೆ.

ನೀವು ಏಕಕಾಲದಲ್ಲಿ ಡೇಟಾ ಮತ್ತು ಸೂಚನೆಗಳನ್ನು

ಪ್ರವೇಶಿಸಲು ಬಯಸಿದರೆ ಪ್ರಯೋಜನವಾಗಿದೆ, ನೀವು

ಅದನ್ನು ಮಾಡಬಹುದು.

ಕೆಳಗಿನ ನಿಯತಾಂಕಗಳನ್ನು ನೀಡಲಾಗಿದೆ.

ಮಿಸ್ 1 ಗಡಿಯಾರದ ಚಕ್ರವಾಗಿದೆ.

ಆದ್ದರಿಂದ, ಇವುಗಳನ್ನು ಒದಗಿಸಿದ ಮಾಹಿತಿಯಾಗಿದೆ

ಮತ್ತು ನಾವು ಸರಾಸರಿ ಆ್ಯಕ್ಸೆಸ್ ಟೈಮ್ ಅನ್ನು

ಹೇಗೆ ಕಂಡುಹಿಡಿಯಬಹುದು ಎಂಬುದನ್ನು ನಾವು ನೋಡುತ್ತೇವೆ.

ಆದ್ದರಿಂದ, ಒಟ್ಟು ಮೆಮೊರಿ ನಲ್ಲಿ ಕಂಡುಬರುವುದಿಲ್ಲ.

ಅಂತೆಯೇ, ಡೇಟಾ ಆಗುತ್ತದೆ.

ಸರಾಸರಿ ಆ್ಯಕ್ಸೆಸ್ ಟೈಮ್ವನ್ನು ತೋರಿಸಿರುವಂತೆ

ಲೆಕ್ಕಹಾಕಲಾಗುತ್ತದೆ.

ಆದ್ದರಿಂದ, ಈ ಉದಾಹರಣೆಯಲ್ಲಿ ಮಿಸ್.

ಆದ್ದರಿಂದ, ನೀವು ಎರಡು ವಿಭಿನ್ನ ಕ್ಯಾಶ್ ಕ್ಕಾಗಿ

ಕಾರ್ಯಕ್ಷಮತೆಯ ಲೆಕ್ಕಾಚಾರವನ್ನು ನೋಡೋಣ.

ಸಾಮಾನ್ಯವಾಗಿ, ನಾವು ಎರಡು ಹಂತದ ಹೈರಾರ್ಕಿ

ಯಲ್ಲಿ, ನಾವು ಕೇವಲ ಎರಡು ಹಂತಗಳನ್ನು ಹೊಂದಿದ್ದೇವೆ

M1 ಮತ್ತು M2, ಆದರೆ ವಾಸ್ತವದಲ್ಲಿ ನಾವು ಬಹು ಹಂತಗಳನ್ನು

ಹೊಂದಿದ್ದೇವೆ.

ಬಹು ಹಂತಗಳಿಗೆ ನಾವು ಎರಡು ಹಂತಗಳಿಗೆ ಏನು

ಮಾಡಿದ್ದೇವೆಯೋ ಅದನ್ನು ಬಹು ಹಂತಗಳಿಗೆ ವಿಸ್ತರಿಸಬಹುದು.

ಆದ್ದರಿಂದ, ನೀವು ಈ ನಿರ್ದಿಷ್ಟ ರೇಖಾಚಿತ್ರವನ್ನು

ನೋಡಿದರೆ ಇದು ಅತ್ಯಂತ ಪ್ರಾಯೋಗಿಕ ಮೆಮೊರಿ

ಸಿಸ್ಟಮ್ ಆಗಿದೆ.

ಆದ್ದರಿಂದ, ನಾವು ಹೇಗೆ ಲೆಕ್ಕ ಹಾಕುತ್ತೇವೆ?

ನಾವು ನೋಡುವಂತೆ ಇದರ ಆ್ಯಕ್ಸೆಸ್ ಟೈಮ್ ಇರುವುದಿಲ್ಲ.

ಡೇಟಾ ಮೂಲಕ ನಿರ್ವಹಿಸಲಾಗುತ್ತದೆ.

ಈಗ, ನಮಗೆ ಇನ್ನೊಂದು ಹಂತವಿದೆ ಎಂದು ನೋಡೋಣ;

ಮೆಮೊರಿ ಹೈರಾರ್ಕಿದಲ್ಲಿ ಕಂಡುಬರುವುದಿಲ್ಲ.

ಆದ್ದರಿಂದ, M2 ನ ಹಿಟ್ನ ಲೆಕ್ಕಾಚಾರವನ್ನು

ಮಾಡಿದ್ದೇವೆ.

ಆ್ಯಕ್ಸೆಸ್ ಟೈಮ್ tA ಅನ್ನು ಈ ಅಭಿವ್ಯಕ್ತಿಯಿಂದ

ನೀಡಲಾಗಿದೆ.

ಆದ್ದರಿಂದ, ಸರಾಸರಿ ಆ್ಯಕ್ಸೆಸ್ ಟೈಮ್ ಎಷ್ಟು?

ಅಭಿವ್ಯಕ್ತಿ ತೋರಿಸಲಾಗಿದೆ.

ಇದು ಮೆಮೊರಿ ಯ ಮೂರು ಹಂತಗಳಿಗೆ ಸಮೀಕರಣವಾಗಿದೆ.

ಆದ್ದರಿಂದ, CPU ಗೆ ಮೆಮೊರಿಗಿಂತ ಭಿನ್ನವಾಗಿರುತ್ತದೆ.

ವಿನಂತಿಸಿದ ಮಾಹಿತಿಯು ಉನ್ನತ ಮಟ್ಟದ ಮೆಮೊರಿ‌ನಲ್ಲಿ

ಅಳವಡಿಸಲಾಗಿದೆ.

ಆದ್ದರಿಂದ, ನಾವು ಏನು ಮಾಡುತ್ತಿದ್ದೇವೆ.

ನಾವು ಮೊದಲು ಉನ್ನತ ಮಟ್ಟದ L1 ಅನ್ನು ಪರಿಶೀಲಿಸುತ್ತಿದ್ದೇವೆ.

ಈ ನಿರ್ದಿಷ್ಟ ಪದವು ಇದೆಯೋ ಇಲ್ಲವೋ ಎಂದು

ನಮಗೆ ಮೊದಲೇ ತಿಳಿದಿರುವ ಯಾವುದೇ ಕಾರ್ಯವಿಧಾನವಿದೆಯೇ

ಅಥವಾ ತಪಾಸಣೆಯನ್ನು ಸ್ವಲ್ಪ ವೇಗವಾಗಿ ಮಾಡಬಹುದು

ಆದ್ದರಿಂದ ಹಿಟ್ ಅನುಷ್ಠಾನವನ್ನು ಹೊಂದಿದ್ದರೆ, ಅದನ್ನು

ಸಮಂಜಸವಾದ ಸಮಯದಲ್ಲಿ ನಿರ್ವಹಿಸಬಹುದು.

ಸತತ ಹಂತಗಳ ನಡುವೆ ಬ್ಲಾಕ್ ಮೂಲಕ ನಿಯಂತ್ರಿಸಬಹುದು.

ಈ ಸಮಯದಲ್ಲಿ ಕೆಲವು ಪ್ರಶ್ನೆಗಳು ಉದ್ಭವಿಸುತ್ತವೆ.

ಒಂದು ಬ್ಲಾಕ್ ಯನ್ನು ಹೊಂದಿದ್ದೇವೆ ಎಂದು

ಹೇಳೋಣ.

ಆದ್ದರಿಂದ, ಮತ್ತೆ ನಾವು ಪ್ರೊಸೆಸರ್ಗಳನ್ನು

ಪಡೆದುಕೊಂಡಿದೆ.

ಈಗ, ನಾವು ಬ್ಲಾಕ್ ಗುರುತಿಸುವಿಕೆ ಸಹ ಮುಖ್ಯವಾಗಿದೆ.

ಅದೇ ರೀತಿ, ಬ್ಲಾಕ್ ಕ್ಕೆ ತರಲಾಗುತ್ತದೆ

ಮತ್ತು ನಂತರ ಅದನ್ನು ಪ್ರವೇಶಿಸಲಾಗುತ್ತದೆ.

ಈಗ ಇದರ ಗಾತ್ರ ಚಿಕ್ಕದಾಗಿದೆ.

ಆದ್ದರಿಂದ, ಒಂದು ಸಮಯದಲ್ಲಿ ಸೀಮಿತ ಸಂಖ್ಯೆಯ ಬ್ಲಾಕ್

ಎಂದು ಕರೆಯಲಾಗುತ್ತದೆ.

ಬರೆಯುವ ತಂತ್ರ ಎಂದರೆ ನಾವು ಬರೆಯುವ ಕಾರ್ಯಾಚರಣೆಯನ್ನು

ನಿರ್ವಹಿಸುವಾಗ ಬರವಣಿಗೆಯಲ್ಲಿ ಏನಾಗುತ್ತದೆ.

ಈ ಬರಹ ಕಾರ್ಯಾಚರಣೆಗೆ ಯಾವ ತಂತ್ರಗಳನ್ನು

ಬಳಸಬೇಕು?

ವಿಶಿಷ್ಟವಾದ ಕಂಪ್ಯೂಟರ್ ಅನ್ನು ಒದಗಿಸುವುದು

ಈ ನಿರ್ದಿಷ್ಟ ಶ್ರೇಣಿಯ ಮುಖ್ಯ ಉದ್ದೇಶವಾಗಿದೆ.

ನಂತರ ನಾವು ಮೈನ್ ಮೆಮೊರಿ ಜಾಗವನ್ನು ಒದಗಿಸುವುದು

ಮುಖ್ಯ ಉದ್ದೇಶವಾಗಿದೆ.

ಆದ್ದರಿಂದ, ಮೂಲಭೂತವಾಗಿ ಈ ವರ್ಚುವಲ್ ಮೆಮೊರಿ

ನಲ್ಲಿ ವಿವರವಾಗಿ ತೆಗೆದುಕೊಳ್ಳಲಾಗುವುದಿಲ್ಲ.

ಇದು ಇಂಟೆಲ್ ಕೋರ್ i ವನ್ನು ಹೊಂದಿದ್ದೇವೆ.

ಮುಂದಿನದು ಕೋರ್-ಐ7 ಸ್ಯಾಂಡಿಬ್ರಿಡ್ಜ್

ನಿಯಂತ್ರಕ, ಇತ್ಯಾದಿ.

ಆದ್ದರಿಂದ, ನಾವು ಉಪನ್ಯಾಸ 29 ರ ಅಂತ್ಯಕ್ಕೆ ಬರುತ್ತೇವೆ,

ಅಲ್ಲಿ ನಾವು ಮೆಮೊರಿ ಒಟ್ಟಾರೆ ಕಾರ್ಯಕ್ಷಮತೆಯ

ಮೇಲೆ ಹೇಗೆ ಪರಿಣಾಮ ಬೀರುತ್ತದೆ ಎಂಬುದನ್ನು

ನಾವು ನೋಡಿದ್ದೇವೆ.

ಧನ್ಯವಾದ.