CH IV-B - Memory II

Reducing the number of TLB misses

It saves time and resources

Distinct virtual addresses point to the same physical address

To accelerate cache reading process

To prevent internal fragmentation

It helps avoid storage wastage

Redundant data in the cache

To expedite cache reading while translation occurs

Increased internal fragmentation

Enabling faster cache hit times

48-bit

Second-level

First-level

To speed up virtual to physical address translation

All of the above

High Performance Architectures

Computer Architecture: A Quantitative Approach

36-bit

Second-level

Physical Memory Size × (PTE size + Virtual Address Size)

To reduce address translation time

Replace the least recently used block (LRU)

To reduce address translation time

To emphasize the high cost of write through

Due to their large size

The system will behave improperly and could lead to errors.

To speed up virtual address to physical address translation.

Valid bit and use bit.

By relying on the operating system to update the TLB entries.

To avoid data inconsistencies between the TLB and the page table.

To avoid system malfunctions due to improper translations.

2

64

The miss rate decreases as the number of words in a block increases.

EC0 = CC + µ × ρ

There is a significant improvement

64 bits

The number of TLB entries is increased

They may store duplicate data for the same physical address

To allow for cache read to begin immediately while tag comparison uses physical addresses

Duplicate data may be stored in the cache

Inversely proportional

Larger caches

Virtual memory replacement is primarily controlled by software, while cache replacement is primarily controlled by hardware

2^32 bytes

To act as the lower-level backing store for main memory

To reduce the time required for data transfer

Duplicate data in the cache

To improve performance by allowing multiple memory accesses to proceed in parallel

Hennessy and Patterson's book on computer architecture

All levels are virtually indexed

Page is fixed-size blocks, while segments are variable-size blocks

Virtual memory is part of memory hierarchy

The points in favor of a larger page size are: decreasing the size of the page table, allowing for larger caches with faster hit times, efficient transfer of larger pages to and from secondary storage, and reducing TLB misses by efficiently mapping more memory.

The main issue is that duplicate addresses in virtual caches, such as when two programs use different virtual addresses for the same physical address, could result in two copies of the same data in the cache. This can lead to inconsistencies, incorrect values, and inefficient memory use.

Using part of the page offset for cache indexing allows cache read to begin immediately while still executing the tag comparison using physical addresses. This approach combines the benefits of both virtual and physical caches, improving cache performance.

By invalidating the TLB after modifying the physical page frame number or protection, the system ensures accurate translations and avoids incorrect lookups in the TLB that may have been affected by the modification.

The points in favor of a smaller page size are: storage conservation by avoiding wasted space when contiguous virtual memory regions are not equal in size to a page multiple, avoiding unused memory in a page (internal fragmentation), and a faster process start-up time for smaller processes.

When two programs share the same data object with virtual caches, the programs may use two different virtual addresses for the same physical address. If not handled carefully, this may result in duplicate copies of the data in the cache and inconsistencies when one copy is modified.

The hierarchy level of caches in Intel Core i7 that is virtually indexed and physically tagged is the L1 data cache.

The main reason in favor of using larger pages is to reduce the size of the page table. Increasing the page size results in fewer pages, which, in turn, reduces the size of the page table.

Principle of locality, which states that programs tend to access similar memory locations over time, is the OS guideline that aims to minimize page faults. By taking advantage of this principle, a system can optimize memory usage and minimize the number of page faults.

Computer Architecture: A Quantitative Approach.

To improve the speed of virtual to physical address translation by reducing the number of memory accesses required.

It reduces the complexity and latency of the cache access mechanism.

To increase memory bandwidth by allowing concurrent access to multiple memory modules.

It allows a program to use more memory than is physically available in the system.

To provide a unique address for each physical location in memory.

The virtual address space is divided into smaller chunks, which are mapped to the physical address space using a two-level TLB.

To reduce memory access times by storing frequently accessed data in faster, smaller caches.

It allows for a very large virtual address space, enabling programs to access a large amount of memory.

By reducing memory access times and increasing memory bandwidth.

To provide additional reading and learning resources for students.

Memory interleaving in memory modules improves memory performance by allowing simultaneous access to multiple memory banks.

A wider memory data bus increases the amount of data that can be transferred in a single clock cycle, thus improving memory bandwidth and overall performance.

DRAM organization involves arranging memory cells in rows and columns for efficient access, reducing access time and enhancing memory performance.

Block duplication effects improve memory performance by reducing the chances of memory conflicts and enhancing memory access speed.

Interleaved memory allows for simultaneous access to multiple memory banks, reducing memory access contention and improving overall memory bandwidth.

Construction technology influences factors like clock speed, latency, and data transfer rates, thereby impacting RAM performance positively.

Block identification involves applying a hash function to the virtual address to create a data structure smaller than the number of virtual pages.

TLB is a cache that stores recent translations of virtual memory to physical memory addresses, reducing the time for address translation.

Block replacement aims to minimize page faults by using the least recently used (LRU) block identification method.

Write-back caching with dirty bit is simpler and more efficient, while write-through is costly but ensures data consistency with memory.

The inverted page table reduces memory overhead by creating a structure proportional to the physical pages in memory, improving efficiency.

The reference bit tracks page access to implement the least recently used (LRU) block replacement policy and optimize memory usage.

Due to the high miss penalty cost, a lower miss rate is preferred over simpler placing algorithms.

Through paged or segmented addressing, using a data structure indexed by the page/segment number that holds the physical address of the block.

It makes the OS prefer a lower miss rate over simpler placing algorithms.

The page table contains the physical page address, which is concatenated with the offset to obtain the final physical address.

Because the miss penalty is very high, and it involves access to slower memory devices.

By allowing blocks to be placed anywhere in memory, using fully associative placement.

When using interleaving of 2 banks, the system becomes 1.19 times faster, and with 4 banks, it becomes 1.39 times faster compared to the original system with simple bus.

Memory interleaving improves system performance by allowing parallel access to multiple banks of memory, thereby reducing the overall latency.

The advantage of quadrupling the memory bus width is that it makes the system 1.22 times faster, but the disadvantage is that it becomes prohibitively expensive and does not yield much better performance than memory interleaving with a 64-bit bus and 4 blocks.

The effective cycle time considering cache and miss penalty for a block of 4 words is 3.63 using a 64-bit bus and interleaving with 4 banks.

The memory interleaving technique is used to increase the memory bandwidth by allowing access to multiple memory banks simultaneously, while the bank interleaving technique is used to reduce the memory latency by distributing memory accesses across different banks.

The advantages of using larger page sizes in virtual memory systems are reduced page table size, improved cache performance, reduced memory fragmentation, and improved system performance with lower overhead.

The TLB ensures accurate translations after a physical page frame number change in the page table by invalidating the TLB entries that map to the old physical page frame number.

DRAM is a type of RAM that stores data in capacitors and requires periodic refresh cycles to maintain the data integrity. It is commonly used in modern computers as the main memory due to its high storage capacity and low cost.

The main difference between synchronous and asynchronous DRAM is that synchronous DRAM operates synchronously with the memory controller clock signal, while asynchronous DRAM operates asynchronously and requires explicit synchronization with the memory controller.

DRAM latency is the time it takes to access data in the DRAM memory. Higher DRAM latency can negatively impact system performance by increasing the overall memory access time.

Using part of the page offset for indexing in caches spreads out the data in the cache more evenly, which helps to mitigate the problem of cache conflicts, reducing the miss rate and improving overall cache performance.

In Intel Core i7, address translation uses a two-level TLB. When a virtual address is presented, the TLB is checked for the corresponding physical address. If not found, the page table is consulted, resulting in a page table walk and a TLB miss. The faster the TLB hit ratio, the better the system performance.

Virtually indexed caches use the virtual address to access the cache, while physically indexed and tagged caches use the physical address. Intel Core i7's L1 cache is virtually indexed and physically tagged, while the L2 and L3 caches are physically indexed and tagged.

Memory interleaving is a technique used to improve memory performance by spreading out memory accesses across multiple memory banks. When using memory interleaving, consecutive words in memory are assigned to different banks, allowing memory access to occur concurrently and improving overall memory performance.

Intel Core i7 uses a three-level cache hierarchy, with L1 being the smallest but fastest, and L3 being the largest but slowest. The benefits of using a multilevel cache hierarchy include improved cache performance and reduced memory latency by effectively managing the cache miss rate at each level.

The number of words in a block, also known as block size, affects the miss rate of a cache system. Generally, increasing block size will reduce the miss rate. However, larger block sizes can lead to higher cache contention, which may negatively impact performance. The optimal block size depends on factors such as cache size, memory latency, and application characteristics.