Register Caching Circuitry for Thread Switch Latency Reduction

Solution Overview

Problem

The frequent switching between threads in computer processing consumes significant processing resources due to the need to save and restore register data, especially as the number of registers grows, leading to increased latency and pressure on data caches.

Innovation Solution

Implementing a register caching system that uses caching circuitry to store valid data for non-executing threads in registers until accessed again, reducing the need for frequent memory accesses and allowing smaller thread execution slices by maintaining valid, modified, and tag fields for registers, thereby handling register saves and restores asynchronously during context switches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If all register data is saved to memory during thread switches, then thread context accuracy is maintained, but processing resources are consumed significantly and latency increases

Engineering Contradiction:

Improvethread context accuracyVSAvoidprocessing resource consumption

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs preliminary actions by pre-loading register data into the register file before thread switches occur. The caching circuitry maintains valid data in registers proactively, so when a thread needs to switch, the data is already prepared and can be restored immediately without waiting for memory reads.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The register file acts as an intermediary between the thread context and memory. Instead of directly saving all register data to memory during context switches, the system uses the register file as a buffer that holds valid data for multiple threads, reducing the frequency and volume of memory accesses.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If register data is saved and restored frequently during thread switches, then context switching is supported, but memory access latency increases

Engineering Contradiction:

Improvecontext switching capabilityVSAvoidmemory access latency

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-loading register data into the register file before thread switches occur. The caching circuitry maintains valid data in registers proactively, so when a thread needs to switch, the data is already prepared and can be restored immediately without waiting for memory reads.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The register file maintains continuous availability of valid register data for multiple threads without requiring continuous memory accesses. Once data is loaded into the register file, it remains available for subsequent thread resumption, eliminating the need for repeated memory reads during context switching operations.

Inventive Principle:

Principle #20Continuity of useful action

3Reliability

If all registers are saved during thread switches, then thread state is preserved accurately, but pressure on data caches increases

Engineering Contradiction:

Improvethread state preservationVSAvoiddata cache pressure

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The system extracts only the necessary register data that needs to be preserved across thread switches and stores it in the register file, rather than saving all register contents to memory. The caching circuitry identifies and retains only the valid data entries that will be needed for thread resumption, reducing the overall data volume handled during context switches.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The system performs preliminary actions by pre-loading register data into the register file before thread switches occur. The caching circuitry maintains valid data in registers proactively, so when a thread needs to switch, the data is already prepared and can be restored immediately without waiting for memory reads.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9817664B2Register caching techniques for thread switches

Publication Date: 2017.11.14 APPLE INC

AI summary

Techniques are disclosed relating to register caching techniques for thread switches. In one embodiment, an apparatus includes a register file and caching circuitry. In this embodiment, the register file includes a plurality of registers and the caching circuitry is configured to store information that indicates threads that correspond to data stored in respective ones of the plurality of registers. In this embodiment, the apparatus is configured to store, at a point in time at which a first register of the plurality of registers includes first valid data corresponding to a first thread, second valid data corresponding to a second thread in a second register of the plurality of registers. In some embodiments, the disclosed techniques may reduce context switch latency, reduce pressure on a data cache, and/or allow smaller slices of thread execution, for example.