Trace Unit Bypass Mode for Processor Instruction Sequencing
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Solution Overview
Problem
Current processor sequencing techniques do not adequately meet the demands for improved performance and reduced power consumption, particularly in portable devices, while maintaining backward compatibility with x86 instruction code.
Innovation Solution
An improved trace unit is introduced, comprising a decoder circuit, cache circuit, and sequencer circuit that optimizes instruction processing by caching sequences of operations, determining when to cache new sequences, and switching between cached and decoded operations to efficiently sequence instructions for execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a sequencer is used to sequence operations from x86 instructions to improve throughput, then instruction execution performance is improved, but power consumption increases
Solution Approach 1:
The trace unit performs preliminary actions by decoding instructions and building basic blocks in advance before execution. The sequencer pre-sequences operations and the cache circuit pre-caches trace data, so that when execution begins, the data is already prepared and available, reducing the need for real-time processing and lowering power consumption during execution.
Solution Approach 2:
The instruction processing is segmented into distinct functional units: a decoder circuit that translates x86 instructions into internal operations, a basic block builder that groups operations into manageable traces, and a sequencer that sequences these traces. This segmentation allows each component to operate independently and efficiently, optimizing both performance and power usage.
2Productivity
If the trace unit sequences operations ahead of the execution unit to improve throughput, then instruction execution performance is improved, but the complexity of the trace unit increases
Solution Approach 1:
The basic block builder serves as an intermediary between the decoder and the sequencer. It receives decoded instructions, groups them into basic blocks (traces), and prepares them for sequencing. This intermediary layer simplifies the overall architecture by breaking down the complex task of instruction sequencing into manageable stages, reducing the complexity burden on any single component.
Solution Approach 2:
The cache circuit is designed to handle multiple functions: caching trace data, managing memory access, and supporting both sequential and random access patterns. By making the cache circuit multi-functional, the design reduces the need for separate dedicated hardware for each function, thereby reducing overall trace unit complexity while maintaining high throughput.
3Productivity
If the cache circuit is used to store sequences of operations to improve performance, then instruction execution throughput is improved, but the device complexity increases
Solution Approach 1:
Instead of creating entirely new trace data, the system uses the cache circuit to store copies of previously executed or predicted trace sequences. When a trace is needed, a copy is retrieved from the cache rather than regenerating it, significantly improving throughput. The cache stores simplified representations of traces, reducing the complexity of managing full instruction sequences.
4Productivity
If the operations fetch circuit switches between cached and decoded operations to optimize performance, then instruction execution throughput is improved, but the control logic complexity increases
Solution Approach 1:
The operations fetch circuit dynamically adapts its behavior based on runtime conditions. It can switch between fetching from the cache (when traces are available) and decoding new instructions (when cache misses occur or optimization opportunities arise). This dynamic adaptability allows the system to optimize throughput without requiring complex static control logic for every possible scenario, as the circuit responds flexibly to actual execution conditions.
Data Source
AI summary
An instruction processing circuit for a processor includes a decoder circuit, a cache circuit, a sequencer circuit operable to select a next sequence of operations, and an operations fetch circuit operable to convey the next sequence of operations to an execution circuit, receive an indication that a sequencing action of the sequencer circuit is sequencing ahead of the execution circuit, and switch, based on the indication, a source of the operations fetch circuit between the cache circuit and the decoder circuit.