Reach Matrix Scheduler Circuit for Processor Instruction Scheduling
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Solution Overview
Problem
Conventional scheduler circuits in processors face challenges in achieving optimal performance due to increased circuit delays and power consumption as the instruction window size grows, particularly in out-of-order execution scenarios where dataflow processing is unpredictable, leading to inefficiencies in scheduling latency and power usage.
Innovation Solution
The implementation of a reach matrix scheduler circuit with N × R matrix wake-up circuits, where 'R' is less than 'N', reduces grant lines and complexity, allowing only 'R' instructions to be woken up by a producer instruction, thereby decreasing timing delays and enabling larger instruction windows without increasing overall scheduling latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the instruction window size is increased to improve instruction-level parallelism, then processor performance is improved, but circuit delays and power consumption increase
Solution Approach 1:
The wake-up circuit is segmented into multiple N×R matrix circuits, each handling a specific range of instructions. Each matrix has N rows for instructions and R columns for grant lines, where R < N. This segmentation reduces the complexity of each individual matrix while maintaining the overall functionality of tracking dependencies across a large instruction window.
Solution Approach 2:
The patent transitions from a conventional N×N matrix wake-up circuit to an N×R matrix with R < N, effectively changing the dimensional structure. By reducing the number of columns from N to R, the circuit achieves the same functional coverage with reduced complexity and shorter critical paths, enabling larger instruction windows without proportional increases in delay.
2Productivity
If the instruction window size is increased to improve instruction-level parallelism, then processor performance is improved, but power consumption increases
Solution Approach 1:
The wake-up circuit is divided into multiple N×R matrix circuits, each processing a subset of instructions. This segmentation reduces the number of active circuit elements that need to be monitored and updated, thereby reducing power consumption while still supporting large instruction windows for high parallelism.
Solution Approach 2:
Instead of implementing a full N×N matrix where every instruction could potentially wake up every other instruction, the patent uses N×R matrices with R < N, implementing only the necessary partial connections. This partial action approach reduces the total number of circuit elements and their associated power consumption while maintaining sufficient functionality for typical dependency patterns.
3Adaptability or versatility
If conventional N×N matrix wake-up circuits are used, then all instructions can be woken up, but scheduling latency increases
Solution Approach 1:
The patent changes the dimensional structure from N×N to N×R matrices with R < N. This dimensional change reduces the number of grant lines and the critical path length in the wake-up circuit, directly reducing scheduling latency. The reduced matrix size means fewer logic stages and shorter signal propagation paths while still providing adequate wake-up capability for practical workloads.
Data Source
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AI summary
A reach matrix scheduler circuit for scheduling instructions to be executed in a processor is disclosed. The scheduler circuit includes an N x R matrix wake-up circuit, where 'N' is the instruction window size of the scheduler circuit, and 'R' is the "reach" with the instruction window of matrix wake-up circuit, with 'R' being less than 'N'. A grant line associated with each instruction request entry in the N x R matrix wake-up circuit is coupled to 'R' other instruction entries among the 'N' instruction entries. When a producer instruction in an instruction request entry is ready for issuance, the grant line associated with the instruction request entry is activated so that any other instruction entries coupled to the grant line (i.e., within the "reach" of the instruction request entry) that consume the produced value generated by the producer instruction are "woken-up" and subsequently indicated as ready to be issued.