Retire Queue Compression for Out-of-Order Processor Performance
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Solution Overview
Problem
In out-of-order processors, the retire queue quickly exhausts its supply of available entries due to complex instructions being broken down into multiple operations, leading to processor stalling and reduced performance.
Innovation Solution
The control logic compresses multiple instruction operations into a single retire queue entry by determining if the operations meet specific conditions such as being dispatched together, not exceeding available fields, and being able to retire together, thereby reducing the number of retire queue entries required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If complex instructions are broken down into multiple operations, then the scheduler and execution units can handle simpler operations, but the retire queue entries are exhausted more quickly
Solution Approach 1:
The patent merges multiple instruction operations into a single retire queue entry when certain conditions are met (same destination register, sequential execution, no speculation). This combining approach allows multiple operations to share one retire queue slot, reducing the total number of entries needed while maintaining correct retirement ordering.
Solution Approach 2:
The retire queue entry is designed to handle multiple operations simultaneously by incorporating fields that can represent multiple destination registers and multiple source registers. This multi-functional entry structure allows a single entry to track the retirement state of several operations that share common characteristics.
2Productivity
If the retire queue size is increased to prevent stalling, then processor performance improves, but the device complexity and resource usage increase
Solution Approach 1:
By combining multiple operations into single retire queue entries, the patent effectively increases the functional capacity of the retire queue without physically expanding its size. This allows the processor to track more operations simultaneously, reducing stalling and improving performance while maintaining a compact queue structure.
Solution Approach 2:
The patent changes the parameter of operations that can be grouped together by introducing specific grouping criteria (same destination register, sequential retirement, no speculation). This parameter-based grouping allows dynamic determination of which operations share retire queue entries, optimizing the balance between queue size and processing capacity.
3Productivity
If multiple operations share a single retire queue entry, then the retire queue efficiency improves, but the difficulty of tracking and managing operations increases
Solution Approach 1:
The retire queue entry is segmented into distinct fields for tracking different aspects of grouped operations: destination register fields, source register fields, completion status bits, and control information. This segmentation allows the complex state of multiple operations to be managed through structured, organized data fields rather than monolithic tracking.
Solution Approach 2:
The patent implements feedback mechanisms where completion status of individual operations within a grouped entry is tracked and used to determine when the entire group can be retired. The completion bits provide continuous feedback about the state of each operation, enabling the retirement logic to make informed decisions about when to free the shared retire queue entry.
Data Source
AI summary
Systems, apparatuses, and methods for compressing multiple instruction operations together into a single retire queue entry are disclosed. A processor includes at least a scheduler, a retire queue, one or more execution units, and control logic. When the control logic detects a given instruction operation being dispatched by the scheduler to an execution unit, the control logic determines if the given instruction operation meets one or more conditions for being compressed with one or more other instruction operations into a single retire queue entry. If the one or more conditions are met, two or more instruction operations are stored together in a single retire queue entry. By compressing multiple instruction operations together into an individual retire queue entry, the retire queue is able to be used more efficiently, and the processor can speculatively execute more instructions without the retire queue exhausting its supply of available entries.