Store Buffer Search Pointer Adjustment for Out-of-Order Execution
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Solution Overview
Problem
Modern processors face challenges in efficiently executing complex instructions such as floating-point operations and load/store operations, which require more execution time and resources, impacting overall throughput and performance, especially in multiprocessor systems where instructions are executed out-of-order.
Innovation Solution
The implementation of an instruction set architecture that includes packed data instructions and execution units capable of performing operations on multiple data elements in parallel, utilizing SIMD technology and out-of-order execution to optimize the execution of instructions in processors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If floating-point operations and load/store operations are executed in conventional sequential manner, then execution accuracy is maintained, but execution time increases and throughput decreases
Solution Approach 1:
The processor segments instructions into multiple types (first type instructions and second type instructions) with different execution characteristics. First type instructions are executed in-order while second type instructions are executed out-of-order, allowing the system to optimize throughput for compatible instructions without compromising correctness of critical operations.
Solution Approach 2:
The processor dynamically selects execution order based on instruction type. The execution unit determines whether to execute instructions in-order or out-of-order based on the specific instruction characteristics, enabling adaptive optimization of execution time and throughput for different operational contexts.
2Speed
If multiple data elements are processed sequentially, then execution simplicity is maintained, but processing speed decreases
Solution Approach 1:
The execution unit merges multiple data elements into a single instruction stream and processes them simultaneously using SIMD technology. This combining approach allows parallel processing of multiple elements without requiring separate execution paths for each element, thus increasing speed while controlling complexity.
Solution Approach 2:
The execution unit is designed with universal capability to handle both scalar operations and vector operations through the same hardware structure. This multi-functionality allows the processor to efficiently process different types of instructions (first type and second type) and multiple data elements without requiring dedicated specialized units for each operation type.
3Productivity
If instructions are executed strictly in-order, then program correctness is ensured, but processor utilization decreases
Solution Approach 1:
The instruction stream is segmented into different categories where first type instructions maintain strict in-order execution for correctness, while second type instructions allow out-of-order execution for improved utilization. This segmentation enables the system to achieve high processor utilization without compromising the correctness of critical operations.
Solution Approach 2:
The execution unit acts as an intermediary that mediates between in-order and out-of-order execution requirements. It determines the appropriate execution order for each instruction based on its type, ensuring that correctness requirements are met while maximizing processor utilization through selective out-of-order execution.
Data Source
AI summary
A processor includes logic to execute an instruction stream out-of-order. The instruction stream is divided into a plurality of strands and its instructions and those within the streams are ordered by program order (PO). The processor further includes logic to identify an oldest undispatched instruction in the instruction stream and record its associated PO as an executed instruction pointer, identify a most recently committed store instruction in the instruction stream and record its associated PO as a store commitment pointer, a search pointer with PO less than the execution instruction pointer, identify a first set of store instructions in a store buffer with PO less than the search pointer and eligible for commitment, evaluate whether the first set of store instructions is larger than a number of read ports of the store buffer, and adjust the search pointer.