Processor Performance Hints for Cache Control
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Solution Overview
Problem
Existing approaches to managing data movement in computer processors are limited by the difficulty in updating page tables, the coarseness of data characterization, and the lack of flexibility, especially when dealing with huge pages and the need for rapid innovation to address new compute requirements.
Innovation Solution
The introduction of portable performance hints that can be easily added to a computer processor using either an immediate-bit-based approach or a register-based approach, allowing for flexible and efficient data movement without requiring changes to the processor's hardware implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If new instructions are added to the instruction set for each data characteristic, then data handling flexibility is improved, but device complexity and validation requirements increase significantly
Solution Approach 1:
The patent changes the parameter representation from discrete instruction types to continuous hint bits within existing instructions. By modifying the immediate field or adding hint bits to existing instruction formats, the system can specify data characteristics (such as prefetch distance, cache line size, data type) without creating new instruction types. This resolves the contradiction by maintaining instruction set simplicity while achieving fine-grained data handling control through parameter variation.
Solution Approach 2:
The patent makes existing instructions universal by adding hint bits that can specify multiple different data characteristics depending on the context. A single instruction format with hint bits can handle various data access patterns (prefetch, load, store) and data types without requiring separate specialized instructions. This multi-functionality approach improves adaptability while avoiding the complexity of expanding the instruction set with multiple new instruction types.
2Measurement precision
If page table updates are used to assign data characteristics, then data type characterization is achieved, but the approach becomes coarse-grained and difficult to update
Solution Approach 1:
The patent applies preliminary action by encoding data characteristics directly in the instruction stream before execution. Instead of updating page tables during runtime to change data characteristics, the hints are embedded in the instructions themselves, allowing the processor to act on these characteristics immediately without requiring subsequent page table modifications. This resolves the contradiction by providing precise data characterization that is easily applied without update difficulties.
Solution Approach 2:
The patent extracts the data characteristic information from the page table structure and embeds it directly in the instruction stream as hint bits. This separation removes the dependency on page table updates for data characterization, allowing precise per-instruction data type specification independent of the memory management structure. The extraction resolves the contradiction by providing precise characterization without the operational burden of page table management.
3Quantity of substance
If huge pages are used for data storage, then memory efficiency is improved, but data characterization becomes even coarser
Solution Approach 1:
The patent applies local quality by allowing different data characteristics to be specified for different instructions accessing the same huge page. While huge pages provide coarse-grained memory allocation, the hint bits in individual instructions provide fine-grained local characterization of data types and access patterns within that page. This resolves the contradiction by maintaining memory efficiency at the page level while achieving precise data characterization at the instruction level.
Data Source
AI summary
Methods, apparatus, and computer programs are disclosed for data/instruction access based on performance hints. In some embodiments, a method comprises decoding an instruction to access data or code by a core of a computer processor, the instruction to provide one or more hints on how the data or code is to be processed through a cache hierarchy of the computer processor based on the instruction, the one or more hints indicating which level of the cache hierarchy or which cache in a level of the cache hierarchy to load or store the data or code, a priority of the data or code in a cache, or how the data or code is to be shared among multiple cores of the computer processor. The method further comprises processing the data or code based on the one or more hints responsive to the decoded instruction.