Streaming Processor Register Allocation by Instruction Latency
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Solution Overview
Problem
Graphics Processing Units (GPUs) face challenges in efficiently managing memory and registers for parallel thread execution, leading to latency issues and increased costs due to the need for additional memory, which complicates the trade-off between register size and execution latency.
Innovation Solution
A streaming processor with general-purpose registers divided into persistent and volatile types, where persistent registers are statically allocated for long-latency operations and volatile registers are dynamically allocated for short-latency operations, allowing for efficient allocation and de-allocation based on instruction latency, thereby optimizing register usage and accommodating more threads with reduced memory size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If additional memory is provided to accommodate more threads, then the number of threads that can be processed increases, but the cost increases and the trade-off between register size and execution latency becomes more complex
Solution Approach 1:
The general-purpose registers are segmented into two distinct types: persistent registers for long-latency operations and volatile registers for short-latency operations. This segmentation allows the system to manage different thread types with appropriate register characteristics, reducing the need for additional memory while accommodating more threads efficiently.
Solution Approach 2:
Different register types are assigned different characteristics tailored to specific operational needs. Persistent registers maintain data across thread switches for long-latency operations, while volatile registers are quickly allocatable and deallocatable for short-latency operations. This local differentiation optimizes register usage for each thread type without requiring uniform memory expansion.
2Loss of time
If register size is increased to reduce latency, then execution latency decreases, but the cost increases and fewer threads can be accommodated
Solution Approach 1:
Registers are divided into persistent and volatile types based on latency requirements. Persistent registers provide fast access for long-latency operations without requiring the entire register file to be large, while volatile registers handle short-latency operations efficiently. This segmentation reduces the overall register size requirement while maintaining low latency for critical operations.
Solution Approach 2:
The system changes the parameter of register persistence by creating two distinct register types with different lifetime characteristics. Persistent registers maintain values across thread switches, effectively reducing latency for operations that span thread boundaries, while volatile registers are rapidly allocated and deallocated. This parameter differentiation allows the system to accommodate more threads with smaller registers.
3Loss of time
If persistent registers are used for long-latency operations, then latency is reduced, but the allocation complexity increases
Solution Approach 1:
The thread scheduler is segmented into specialized components: one handler for persistent register allocation and another for volatile register allocation. This segmentation simplifies the overall allocation complexity by addressing each register type with tailored allocation logic, reducing the cognitive and computational burden of managing mixed register types.
Solution Approach 2:
Persistent registers automatically maintain their values across thread switches without requiring explicit preservation operations, while volatile registers are automatically deallocated when threads switch. This self-service behavior reduces the complexity of register management by eliminating manual intervention for data preservation and cleanup.
4Productivity
If volatile registers are dynamically allocated for short-latency operations, then register utilization efficiency increases, but the management overhead increases
Solution Approach 1:
Volatile registers are designed to be automatically allocated and deallocated by the thread scheduler without requiring complex management routines. When a thread switches, its volatile registers are automatically released for reuse, and new volatile registers are automatically assigned to the incoming thread. This self-service mechanism maximizes register utilization efficiency while minimizing management overhead.
Solution Approach 2:
Volatile registers are quickly discarded when threads switch and immediately recovered for reuse. This rapid discard and recover cycle enables high register utilization efficiency for short-latency operations, as the same physical registers can serve multiple threads in succession without complex preservation or restoration procedures.
Data Source
AI summary
Systems and techniques are disclosed for general purpose register dynamic allocation based on latency associated with of instructions in processor threads. A streaming processor can include a general purpose registers configured to stored data associated with threads, and a thread scheduler configured to receive allocation information for the general purpose registers, the information describing general purpose registers that are to be assigned as persistent general purpose registers (pGPRs) and volatile general purpose registers (vGPRs). The plurality of general purpose registers can be allocated according to the received information. The streaming processor can include the general purpose registers allocated according to the received information, the allocated based on execution latencies of instructions included in the threads.