Processor Pointer Extent Fields for Accurate Cache Prefetching
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Solution Overview
Problem
Existing processors face challenges in accurately prefetching data, leading to reduced performance and increased power consumption due to incorrect predictions about data needs.
Innovation Solution
Incorporating a data object extent field in a 64-bit pointer to provide information about the extent of a data object, allowing predictors to make informed decisions on prefetching additional cache lines and address translation unit operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If prefetching is performed based on historical data and statistical algorithms, then data may be loaded into cache before needed, but incorrect predictions cause performance reduction and increased power consumption
Solution Approach 1:
The patent applies preliminary action by adding extent information to pointers before data access operations. This extent metadata is prepared in advance and stored with the pointer, enabling the prefetcher to make informed decisions about data prefetching without requiring extensive historical analysis or statistical computations during runtime.
Solution Approach 2:
The patent introduces extent information as an intermediary element between the pointer and the prefetcher. This intermediate metadata structure provides direct information about data object boundaries and sizes, acting as a mediator that translates pointer information into actionable prefetching decisions without requiring complex prediction algorithms.
2Reliability
If prefetching is performed based on historical data and statistical algorithms, then data may be loaded into cache before needed, but incorrect predictions cause unnecessary cache evictions of needed data
Solution Approach 1:
The patent applies preliminary action by adding extent information to pointers before data access operations. This extent metadata is prepared in advance and stored with the pointer, enabling the prefetcher to make informed decisions about data prefetching without requiring extensive historical analysis or statistical computations during runtime.
Solution Approach 2:
The patent implements feedback by using extent information from accessed data objects to refine and improve prefetching decisions. The system learns from the actual extent of data objects that are accessed, using this feedback to adjust prefetching behavior and avoid bringing in unnecessary data that would evict needed cache lines.
3Reliability
If extent information is added to pointers, then prefetching decisions can be improved, but pointer structure complexity increases
Solution Approach 1:
The patent applies merging by combining the pointer and extent information into a unified pointer structure. Rather than maintaining separate pointer and metadata structures, the extent information is integrated directly into the pointer representation, reducing overall system complexity despite the added information.
Solution Approach 2:
The patent applies universality by designing the extended pointer structure to serve multiple functions: it provides both the traditional addressing capability of pointers and additional extent information for prefetching, optimization, and memory management decisions, making the structure multi-functional and reducing the need for separate specialized structures.
Data Source
AI summary
A processor of an aspect includes a cache hierarchy and a memory access unit coupled with the cache hierarchy. The memory access unit is to perform a demand load based on a Y-bit pointer to cause a first one or more cache lines to be loaded from memory into the cache hierarchy. The Y-bit pointer has an X-bit virtual address field and a data object extent field in one or more of bits [Y-1:X]. The data object extent field is to store a value. The processor also includes a prefetch unit coupled with the cache hierarchy. The prefetch unit is to determine whether or not to prefetch a second one or more cache lines, adjacent to the first one or more cache lines, from memory into the cache hierarchy based at least in part on the value. In another aspect, the prefetch unit may additionally or alternatively scan code or data for a bit pattern in bits [Y-1:X] to identify likely pointers and prefetch data referenced by such identified pointer's memory addresses. Other processors, methods, systems, and instructions are disclosed.