Asynchronous ALU Pipeline for GPU Throughput
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Solution Overview
Problem
Massively multithreaded machines employing a single instruction-multiple thread (SIMT) execution model, such as GPUs, are limited by deterministic execution latency of vector arithmetic instructions, which restricts peak computational throughput and increases power and area requirements of vector arithmetic logic units.
Innovation Solution
Integration of a self-timed, asynchronous ALU pipeline into a synchronous SIMD pipeline unit, along with interface logic and circuits for communication between the asynchronous ALU and synchronous vector register file and instruction scheduler, allowing asynchronous scheduling and reducing dependency on worst-case execution latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a synchronous vector ALU with deterministic execution latency is used, then the execution latency is predictable, but the peak computational throughput is limited and power/area requirements increase
Solution Approach 1:
The patent transitions from a static synchronous ALU with fixed pipeline stages to a dynamic asynchronous ALU where execution latency varies based on actual data dependencies and operation complexity. The asynchronous pipeline allows each instruction to complete in variable time rather than being constrained by the worst-case latency of all instructions, thereby increasing peak throughput while maintaining reliability through proper synchronization mechanisms at interface points.
2Reliability
If a synchronous vector ALU with deterministic execution latency is used, then the bypass path latency is fixed, but the power and area requirements increase
Solution Approach 1:
The patent changes the fundamental parameter of latency from a fixed deterministic value to a variable asynchronous value. By eliminating the need for fixed pipeline stages and associated bypass logic, the design reduces the power and area requirements of the vector ALU while maintaining correctness through asynchronous handshaking protocols that dynamically determine when data is ready.
3Productivity
If asynchronous ALU pipeline is integrated, then peak throughput is enhanced and power/area requirements are reduced, but execution latency becomes non-deterministic
Solution Approach 1:
The patent introduces intermediary synchronization mechanisms at the interface between the asynchronous ALU pipeline and the synchronous SIMD pipeline unit. These intermediaries include completion status registers and instruction picker logic that translate the non-deterministic asynchronous execution into deterministic instruction issuance, allowing the system to achieve high throughput while maintaining the predictability required by the host processor.
4Productivity
If asynchronous scheduling is implemented, then instruction execution efficiency is improved, but interface logic and circuit complexity increase
Solution Approach 1:
The patent segments the interface logic into distinct functional blocks: an instruction scheduler that queues instructions, a completion status register that tracks ALU execution state, and an instruction picker that selects ready instructions for execution. This segmentation manages complexity by localizing synchronization requirements to specific interface points rather than requiring complex logic throughout the entire data path.
Data Source
AI summary
A method and apparatus of asynchronous scheduling in a graphics device includes sending one or more instructions from an instruction scheduler to one or more instruction first-in/first-out (FIFO) devices. An instruction in the one or more FIFO devices is selected for execution by a single-instruction/multiple-data (SIMD) pipeline unit. It is determined whether all operands for the selected instruction are available for execution of the instruction, and if all the operands are available, the selected instruction is executed on the SIMD pipeline unit. The self-timed arithmetic pipeline unit (SIMD pipeline unit) is effectively encapsulated in a synchronous, (e.g., clocked by global clock), scheduler and register file environment.