Vector Mask Dependency Chaining for Lower Dataflow Latency
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Solution Overview
Problem
Existing integrated circuit designs face challenges in efficiently processing vector instructions due to the complexity of handling partial mask results and dependencies between vector micro-operations, particularly in out-of-order processors, which leads to increased latency and inefficiencies in register usage.
Innovation Solution
The implementation of a mask unit with associated valid and dependency bits for tracking and chaining vector micro-operations, along with a physical register file accumulator, optimizes the handling of partial mask results by forwarding them to dedicated registers and enabling efficient dependency tracking and merging of micro-operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional register file approaches are used to handle vector instructions, then implementation is simpler, but dataflow latency increases and processing efficiency deteriorates
Solution Approach 1:
The patent implements preliminary action by forwarding partial mask results from executed micro-operations to the mask register file before all micro-operations complete. This allows subsequent micro-operations to access and utilize these partial results immediately, eliminating wait states and reducing dataflow latency in the vector instruction processing pipeline.
Solution Approach 2:
The patent segments the mask register file into multiple independent banks (e.g., four banks) that can be accessed simultaneously. This segmentation allows parallel access to different portions of mask data, enabling multiple micro-operations to proceed concurrently without blocking each other, thereby improving overall processing throughput and reducing effective latency.
2Productivity
If partial mask results are held until all micro-operations complete, then register usage is simpler, but processing throughput decreases
Solution Approach 1:
The patent implements feedback mechanisms through valid bits and dependency bits associated with each mask register entry. These bits provide real-time status information about the completion state and dependency relationships of micro-operations. The feedback enables the dispatch unit to make informed decisions about which micro-operations can proceed, optimizing throughput while maintaining correct dependency ordering.
Solution Approach 2:
The patent introduces intermediary structures including the mask register file with its associated valid and dependency bits, which act as mediators between executing micro-operations and the instruction dispatch mechanism. These intermediaries buffer and manage partial results, allowing the complex dependency tracking to be isolated from the main execution path while still enabling high throughput processing.
3Reliability
If mask registers are written only after all micro-operations complete, then data consistency is simpler to maintain, but instruction execution latency increases
Solution Approach 1:
The patent performs preliminary writing of partial mask results to the mask register file as micro-operations complete, rather than waiting for all micro-operations to finish. The valid bits track which entries contain valid partial results, ensuring data consistency is maintained through this incremental write approach while significantly reducing the latency for subsequent operations that need these mask values.
Data Source
AI summary
Apparatus and methods for dependency tracking, chaining, and/or fusing for vector instructions. A system, processor, or integrated circuit includes a renamer to generate a valid bit mask for each micro-operation decoded from a first vector instruction, where the valid bit mask indicates what portion of a mask register to write and generate a dependency bit mask for each micro-operation decoded from a second vector instruction, where the dependency bit mask is based on a relationship between the first vector instruction and the second vector instruction, and an issue queue configured to issue for execution each micro-operation from the second vector instruction when an associated dependency bit mask is cleared based on execution of appropriate micro-operations from the first vector instruction.