Processor Load Atomicity Segmentation for TSO Memory Ordering

Solution Overview

Problem

Existing processors face performance bottlenecks due to stricter memory ordering models, particularly Total Store Ordering (TSO), when executing multiple register loads and vector loads, as they often require all bytes to be sourced from a single source, leading to slower execution and potential incorrect order observations.

Innovation Solution

Implementing a smaller atomicity size than the operation size for memory consistency order, specifically for multiple register loads and vector loads, ensuring each atomic element is sourced from a single source before completion, thereby allowing out-of-order execution without violating TSO.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a processor executes multiple register loads or vector loads with large operation size, then the operation can process more data in parallel, but it becomes less likely to obtain all bytes from a single source, requiring slower execution to maintain atomicity for stricter ordering models

Engineering Contradiction:

Improveload execution throughputVSAvoidload execution speed

Core Design Contradiction:

ProductivityVSSpeed

Solution Approach 1:

The patent segments the atomicity requirement into smaller units by introducing an atomicity size parameter that is independent of the operation size. For multiple register loads and vector loads, the atomicity size can be smaller than the total operation size, allowing the operation to be divided into smaller atomic elements that can be sourced independently from different sources while still maintaining memory consistency guarantees.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameter of atomicity size from being fixed to being configurable and instruction-specific. By allowing the atomicity size to differ from the operation size, the system can optimize performance for different types of load operations while maintaining correctness for stricter ordering models like TSO.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the processor enforces that all bytes of a load operation must be sourced from a single source to maintain TSO, then memory consistency is guaranteed, but performance suffers due to slower execution and potential retries

Engineering Contradiction:

Improvememory consistency guaranteeVSAvoidload execution throughput

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent segments the atomicity requirement into smaller units by introducing an atomicity size parameter that is independent of the operation size. For multiple register loads and vector loads, the atomicity size can be smaller than the total operation size, allowing the operation to be divided into smaller atomic elements that can be sourced independently from different sources while still maintaining memory consistency guarantees.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameter of atomicity size from being fixed to being configurable and instruction-specific. By allowing the atomicity size to differ from the operation size, the system can optimize performance for different types of load operations while maintaining correctness for stricter ordering models like TSO.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If the processor uses a smaller atomicity size than operation size for multiple register loads and vector loads, then loads can complete without retries or flushes improving performance, but it becomes more complex to track and verify single-source requirements for each atomic element

Engineering Contradiction:

Improveload execution throughputVSAvoidatomicity tracking complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent segments the atomicity requirement into smaller units by introducing an atomicity size parameter that is independent of the operation size. For multiple register loads and vector loads, the atomicity size can be smaller than the total operation size, allowing the operation to be divided into smaller atomic elements that can be sourced independently from different sources while still maintaining memory consistency guarantees.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces an intermediary mechanism in the load/store unit that automatically tracks and verifies the source of each atomic element. This intermediary structure manages the complexity of tracking multiple sources for different atomic elements within a single load operation, offloading the verification burden from the control logic.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12530295B2Decoupling atomicity from operation size

Publication Date: 2026.01.20 APPLE INC

AI summary

In an embodiment, a processor implements a different atomicity size (for memory consistency order) than the operation size. More particularly, the processor may implement a smaller atomicity size than the operation size. For example, for multiple register loads, the atomicity size may be the register size. In another example, the vector element size may be the atomicity size for vector load instructions. In yet another example, multiple contiguous vector elements, but fewer than all the vector elements in a vector register, may be the atomicity size for vector load instructions.