Speculative Interrupt Vector Prefetching in Processor Pipelines

Solution Overview

Problem

In processor systems, memory access latency occurs when an interrupt handler is not cached, leading to reduced processor performance due to lengthy miss and fetch operations, and locking interrupt handlers in the cache reduces cache size, further impacting performance.

Innovation Solution

Detecting exceptional conditions in the instruction pipeline, prefetching interrupt handler instructions from storage above the instruction cache before the processor accepts the interrupt, ensuring the instructions are available in the cache by the time the interrupt is processed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If interrupt handlers are locked in the instruction cache, then memory access latency is reduced, but cache size is effectively reduced

Engineering Contradiction:

Improvememory access latencyVSAvoidcache size

Core Design Contradiction:

Loss of timeVSVolume of stationary object

Solution Approach 1:

The system performs preliminary actions by detecting exceptional conditions in the instruction pipeline and speculatively prefetching interrupt handler instructions from storage above the instruction cache before the processor actually accepts the interrupt. This ensures the instructions are already in the cache by the time they are needed, reducing memory access latency without requiring permanent locking of cache space.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system dynamically adjusts cache content based on runtime conditions. Instead of statically locking interrupt handlers in the cache, the system uses exception detection logic to identify when interrupt handlers are needed and dynamically loads them into the cache only when exceptional conditions are detected, making the cache allocation adaptive rather than fixed.

Inventive Principle:

Principle #15Dynamics

2Volume of stationary object

If interrupt handlers are not cached, then cache size is maintained, but memory access latency increases due to lengthy miss and fetch operations

Engineering Contradiction:

Improvecache sizeVSAvoidmemory access latency

Core Design Contradiction:

Volume of stationary objectVSLoss of time

Solution Approach 1:

The system performs preliminary actions by detecting exceptional conditions in the instruction pipeline and speculatively prefetching interrupt handler instructions from storage above the instruction cache before the processor actually accepts the interrupt. This ensures the instructions are already in the cache by the time they are needed, reducing memory access latency without requiring permanent locking of cache space.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system enables the cache to service itself by implementing exception detection logic that automatically identifies when interrupt handlers are needed and triggers prefetching operations. The cache management system monitors pipeline stages and autonomously loads required instructions, eliminating the need for external control or manual intervention.

Inventive Principle:

Principle #25Self-service

3Loss of time

If speculative prefetching is implemented, then memory access latency is reduced, but processor complexity increases

Engineering Contradiction:

Improvememory access latencyVSAvoidprocessor complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The system introduces an intermediary prefetching mechanism that sits between the exception detection logic and the instruction cache. The exception detection logic identifies exceptional conditions and generates prefetch requests, which are handled by the prefetching mechanism that retrieves instructions from storage above the cache and loads them into the cache, mediating between detection and execution.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system enables the cache to service itself by implementing exception detection logic that automatically identifies when interrupt handlers are needed and triggers prefetching operations. The cache management system monitors pipeline stages and autonomously loads required instructions, eliminating the need for external control or manual intervention.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS8291202B2Apparatus and methods for speculative interrupt vector prefetching

Publication Date: 2012.10.16 QUALCOMM INC

AI summary

Techniques for interrupt processing are described. An exceptional condition is detected in one or more stages of an instruction pipeline in a processor. In response to the detected exceptional condition and prior to the processor accepting an interrupt in response to the detected exceptional condition, an instruction cache is checked for the presence of an instruction at a starting address of an interrupt handler. The instruction at the starting address of the interrupt vector table is prefetched from storage above the instruction cache when the instruction is not present in the instruction cache to load the instruction in the instruction cache, whereby the instruction is made available in the instruction cache by the time the processor accepts the interrupt in response to the detected exceptional condition.