Concurrent Complex-Instruction Decoding for Wider Frontend Throughput
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Solution Overview
Problem
Modern processors face challenges in efficiently decoding complex instructions, which often require multiple decoded instructions, leading to inefficiencies in decode circuitry design and performance.
Innovation Solution
The processor incorporates decode circuitry capable of concurrently decoding multiple complex instructions, utilizing a combination of programmable logic array (PLA) based and read-only memory (ROM) based mechanisms to handle different types of complex instructions, allowing for wider frontend issue bandwidth and improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single shared decode unit is used to decode all complex instructions, then device complexity is reduced, but decode throughput and productivity deteriorate due to contention and serial processing
Solution Approach 1:
The decode circuitry is segmented into multiple independent decode units (first decode unit, second decode unit, third decode unit) that can concurrently decode different complex instructions. Each decode unit is dedicated to specific instruction types or decoding tasks, eliminating serial processing constraints and enabling parallel decoding operations that significantly improve throughput.
Solution Approach 2:
The patent transitions from a single-dimensional serial decoding approach to a multi-dimensional parallel decoding architecture. By introducing multiple decode units operating simultaneously across different instruction streams, the system adds a temporal and spatial dimension to the decoding process, enabling wider frontend issue bandwidth.
2Device complexity
If multiple complex instructions are decoded sequentially, then device complexity remains low, but loss of time increases due to serial processing latency
Solution Approach 1:
Multiple complex instructions are fetched and prepared for decoding in advance while previous instructions are still being processed. The pipeline architecture allows overlapping of instruction preparation and execution phases, reducing the effective latency by performing preliminary actions before critical path completion.
Solution Approach 2:
The decode pipeline maintains continuous useful action by ensuring that while one decode unit is processing an instruction, other decode units are simultaneously processing different instructions. This eliminates idle cycles and maintains steady-state decoding throughput, minimizing time loss compared to sequential processing.
3Productivity
If decode circuitry is designed for high throughput, then productivity improves, but device complexity increases due to multiple decode units and shared resources
Solution Approach 1:
The decode units are designed with universal capabilities to handle multiple types of complex instructions through programmable logic arrays (PLAs). Each decode unit can be configured to decode different instruction sets, making the hardware more versatile and reducing the need for entirely separate dedicated decoding circuits for each instruction type.
Solution Approach 2:
Instead of creating entirely new decoding hardware for each instruction type, the patent uses programmable logic arrays that can be programmed or configured to decode different instruction sets. This copying approach allows multiple decode units to share common hardware resources while maintaining specialized functionality, balancing performance with complexity.
Data Source
AI summary
A processor of an aspect includes decode circuitry to decode a first subset of instructions and a second subset of instructions. The decode circuitry is to concurrently decode at least two instructions of the first subset of instructions. The first subset of instructions is to be decoded into varying numbers of decoded instructions ranging from at least two to at least ten. The decode circuitry is only able to decode fewer instructions of the second subset of instructions at a time than the at least two instructions of the first subset of instructions. Each of the second subset of instructions is to be decoded into at least two decoded instructions. The processor also includes circuitry coupled with the decode circuitry to receive decoded instructions from the decode circuitry. Other processors, methods, systems, and instructions are disclosed.