Dynamic Port Remapping for Out-of-Order Microprocessor Deadlock Avoidance
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Solution Overview
Problem
Conventional out-of-order microprocessor designs face inefficiencies and potential deadlocks due to static mapping of select ports to execution units, leading to load imbalances and reduced dispatch rates when physical register files become full.
Innovation Solution
Implementing a dynamic port remapping scheme where select ports are tied to virtual execution ports, allowing remapping to different physical register units when a register file is full, ensuring instructions are routed to available units and preventing deadlocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If static mapping of select ports to execution units is used, then device complexity is reduced, but productivity decreases due to deadlocks and load imbalances when physical register files become full
Solution Approach 1:
The patent implements dynamic port remapping where the mapping between select ports and execution units is no longer static but changes based on the current state of physical register files. When a register file becomes full, the system dynamically remaps select ports to alternative execution units that have available register capacity, thereby maintaining high instruction dispatch rates without requiring complex static reservation of resources.
Solution Approach 2:
The system changes the mapping parameter (which execution unit a select port connects to) based on the capacity parameter of physical register files. When register file capacity changes (from available to full), the mapping parameter is updated to maintain optimal productivity, transforming a static configuration into an adaptive one that responds to runtime conditions.
2Ease of operation
If select ports are statically tied to execution units, then ease of operation is improved, but reliability decreases due to potential deadlocks when register files are full
Solution Approach 1:
The patent introduces an intermediary remapping layer between select ports and execution units. This intermediary component monitors the capacity of physical register files and dynamically adjusts the mapping to prevent deadlocks. The intermediary maintains ease of operation by abstracting the complexity away from the select logic while ensuring reliability through adaptive remapping when register files become full.
Solution Approach 2:
The system transitions from a static port-to-execution-unit mapping to a dynamic mapping that adapts based on register file capacity. This dynamic behavior ensures reliability by preventing deadlocks while maintaining operational simplicity through automated remapping logic that handles the complexity internally.
3Area of stationary object
If physical register files are distributed into multiple units, then area is reduced, but productivity decreases due to load imbalances between units
Solution Approach 1:
The patent implements dynamic load balancing across distributed physical register file units by remapping select ports based on the current capacity of each unit. When one register file unit becomes full, the system dynamically redirects instructions to alternative execution units with available capacity, thereby maintaining balanced load distribution and maximizing throughput across all distributed units.
Solution Approach 2:
The system changes the mapping parameters between select ports and execution units based on the capacity parameters of distributed register file units. This adaptive remapping ensures that instructions are distributed evenly across all available units, preventing load imbalances and maximizing the productivity benefit of the distributed architecture.
4Device complexity
If static port mapping is used, then device complexity is reduced, but loss of time increases due to pipeline flushes when deadlocks occur
Solution Approach 1:
The patent implements dynamic remapping logic that proactively prevents deadlocks by monitoring register file capacity and redirecting instructions before deadlock conditions occur. This dynamic approach eliminates pipeline flushes and their associated time losses, with the added complexity of remapping logic being far less costly than repeated pipeline flushes and recovery operations.
Solution Approach 2:
The system performs preliminary remapping actions based on predicted or current register file capacity conditions, preventing deadlock situations before they occur. By proactively redirecting instructions to available execution units, the system avoids the time loss associated with pipeline flushes and restarts, making the preliminary remapping complexity worthwhile.
Data Source
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AI summary
A method for performing dynamic port remapping during instruction scheduling in an out of order microprocessor is disclosed. The method comprises selecting and dispatching a plurality of instructions from a plurality of select ports in a scheduler module in first clock cycle. Next, it comprises determining if a first physical register file unit has capacity to support instructions dispatched in the first clock cycle. Further, it comprises supplying a response back to logic circuitry between the plurality of select ports and a plurality of execution ports, wherein the logic circuitry is operable to re -map select ports in the scheduler module to execution ports based on the response. Finally, responsive to a determination that the first physical register file unit is full, the method comprises re -mapping at least one select port connecting with an execution unit in the first physical register file unit to a second physical register file unit.