Pipeline Stage Scheduling for Complex Instruction Execution
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Solution Overview
Problem
Existing data processing apparatus face challenges in efficiently executing complex instructions without increasing pipeline depth or complexity in issue stage circuitry, as dedicated execution pipelines for complex instructions can lead to longer execution times for simple instructions and increased complexity in handling complex instructions.
Innovation Solution
Implementing a data processing apparatus with a plurality of execution pipelines, where the issue circuitry schedules only the first operation of a complex instruction and delegates subsequent operation scheduling to the relevant pipeline stages, using control signals to indicate additional operations, thereby keeping pipeline depth small and avoiding increased complexity in issue stage circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a dedicated execution pipeline is provided for complex instructions, then complex instructions can be executed, but pipeline depth increases and simple instructions experience increased latency
Solution Approach 1:
The execution pipeline is designed to be universal, handling both simple instructions and complex instructions through the same pipeline stages. The pipeline can execute simple operations directly and also manage complex multi-operation sequences by scheduling operations across different pipeline stages, eliminating the need for separate dedicated pipelines for complex instructions.
Solution Approach 2:
Complex instructions are segmented into multiple individual operations that can be scheduled and executed separately across different pipeline stages. Each operation in the sequence is treated as an independent scheduling unit, allowing the pipeline to manage complex instructions through multiple smaller execution steps rather than requiring a dedicated pipeline for the entire complex operation.
2Adaptability or versatility
If a dedicated execution pipeline is provided for complex instructions, then complex instructions can be executed, but execution time for simple instructions increases
Solution Approach 1:
The execution pipeline is designed to be universal, handling both simple instructions and complex instructions through the same pipeline stages. The pipeline can execute simple operations directly and also manage complex multi-operation sequences by scheduling operations across different pipeline stages, eliminating the need for separate dedicated pipelines for complex instructions.
Solution Approach 2:
The pipeline scheduling mechanism is dynamic, allowing flexible allocation of operations to pipeline stages based on the instruction type. Simple instructions can be executed immediately in available pipeline stages, while complex instructions are broken down and scheduled across multiple stages, enabling the system to adapt execution time based on instruction complexity rather than using a fixed long pipeline for all instructions.
3Ease of operation
If issue stage circuitry schedules all operations in a complex instruction sequence, then scheduling control is centralized, but issue stage circuitry complexity increases
Solution Approach 1:
The scheduling responsibility for subsequent operations in a complex instruction sequence is extracted from the issue stage circuitry and transferred to the execution pipeline itself. The pipeline stages are equipped with the capability to schedule their own operations based on the sequence definition, reducing the scheduling burden on the issue stage circuitry while maintaining centralized control for the first operation.
Solution Approach 2:
The execution pipeline is designed to be self-sufficient for scheduling its own operations. Once the first operation is scheduled by the issue stage circuitry, the pipeline uses its internal resources and the sequence definition to automatically schedule subsequent operations without requiring continuous intervention from the issue stage circuitry, thereby reducing issue stage complexity.
4Loss of time
If pipeline depth is reduced, then simple instructions have lower latency, but complex instruction execution becomes more difficult
Solution Approach 1:
Complex instructions are segmented into multiple individual operations that can be scheduled and executed separately across different pipeline stages. Each operation in the sequence is treated as an independent scheduling unit, allowing the pipeline to manage complex instructions through multiple smaller execution steps rather than requiring a dedicated pipeline for the entire complex operation.
Solution Approach 2:
The pipeline scheduling mechanism is dynamic, allowing flexible allocation of operations to pipeline stages based on the instruction type. Simple instructions can be executed immediately in available pipeline stages, while complex instructions are broken down and scheduled across multiple stages, enabling the system to adapt execution time based on instruction complexity rather than using a fixed long pipeline for all instructions.
Data Source
AI summary
A data processing apparatus and method are provided for executing complex instructions. The data processing apparatus executes instructions defining operations to be performed by the data processing apparatus, those instructions including at least one complex instruction defining a sequence of operations to be performed. The data processing apparatus comprises a plurality of execution pipelines, each execution pipeline having a plurality of pipeline stages and arranged to perform at least one associated operation. Issue circuitry interfaces with the plurality of execution pipelines and is used to schedule performance of the operations defined by the instructions. For the at least one complex instruction, the issue circuitry is arranged to schedule a first operation in the sequence, and to issue control signals to one of the execution pipelines with which that first operation is associated, those control signals including an indication of each additional operation in the sequence. Then, when performance of the first operation reaches a predetermined pipeline stage in that execution pipeline, that predetermined pipeline stage is arranged to schedule a next operation in the sequence, and to issue additional control signals to a further one of the execution pipelines with which that next operation is associated in order to cause that next operation to be performed. This has been found to provide a particularly efficient mechanism for handling the execution of complex instructions without the need to provide dedicated execution pipelines for those complex instructions, and without an increase in complexity of the issue circuitry.