Hardware-Assisted Multi-Threaded Register Bank Segmentation
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Solution Overview
Problem
Conventional multi-threaded processors incur significant clock cycles during thread switching due to the need to swap register and data contents between threads, leading to inefficiencies and increased processor requirements for achieving line rate processing in routers, especially when dealing with high-latency memory operations.
Innovation Solution
A hardware-assisted thread switching mechanism that stores all thread contents in a larger register bank and data RAM, allowing for rapid switching by reserving and accessing specific slices or windows based on thread IDs, thereby reducing the need for swapping and minimizing clock cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional multi-threaded processors swap register and data contents between threads, then thread switching can be achieved, but the number of clock cycles required for thread switching increases significantly
Solution Approach 1:
The register bank is divided into multiple segments or slices, with each segment associated with a specific thread. When switching threads, the processor simply switches between different segments of the register bank rather than swapping entire register contents. This segmentation allows rapid thread switching by only changing the active segment pointer, eliminating the need for time-consuming data movement between threads.
Solution Approach 2:
Register segments for multiple threads are pre-configured and allocated before thread switching occurs. Each thread has its dedicated register segment already prepared and positioned in the register bank. When a thread switch is needed, the processor immediately activates the pre-prepared segment for the new thread without requiring any intermediate swapping operations, thus reducing switching time to minimal clock cycles.
2Loss of time
If thread contents are stored in larger on-chip memories to reduce swapping, then clock cycles for swapping are reduced, but the device complexity and cost increase
Solution Approach 1:
The register bank structure serves multiple functions: it stores registers for multiple threads simultaneously, provides dedicated segments for each thread, and enables rapid switching through segment selection. This multi-functional design eliminates the need for separate storage structures for different threads, reducing overall device complexity while maintaining the ability to rapidly switch between threads using the same physical register bank infrastructure.
Solution Approach 2:
The patent merges the register storage for multiple threads into a single unified register bank structure, where different segments of the same register bank serve different threads. This consolidation eliminates the need for separate register files for each thread and removes the requirement for complex swapping mechanisms, thereby reducing device complexity while achieving fast thread switching through simple segment switching.
3Productivity
If more processors are deployed to achieve line rate processing, then processing capacity increases, but the cost and resource requirements increase
Solution Approach 1:
The processor enables self-service multi-threading by maintaining multiple thread contexts within a single processor unit. Each thread has its own register segment and can be switched to rapidly, allowing the single processor to service multiple threads efficiently without requiring additional processor units. This self-service capability allows the processor to achieve line rate processing for multiple streams independently, reducing the total quantity of processors needed.
Data Source
AI summary
Techniques for processing each of multiple threads that share a core processor include receiving an intra-thread register address from the core processor. This address contains C bits for accessing each of 2c registers for each thread. A thread ID is received from a thread scheduler external to the core processor. The Thread ID contains T bits for indicating a particular thread for up to 2T threads. A particular register is accessed in a register bank that has 2(C+T) registers using an inter-thread address that includes both the intra-thread register address and the thread ID. The particular register holds contents for the intra-thread register address for a thread having the thread ID. Consequently, register contents of all registers of all threads reside in the register bank. Thread switching is accomplished rapidly by simply accessing different slices in the register bank, without swapping contents between a set of registers and memory.