Dynamic Branch Micro-operations Cache with Auxiliary Vector
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Solution Overview
Problem
Existing processor systems face inefficiencies in handling conditional branch instructions, leading to costly mispredictions that result in invalidation of micro-operations cache lines and increased power consumption, particularly in contexts like network packet processing where branch predictions are frequently incorrect.
Innovation Solution
The implementation of a micro-operations cache with an auxiliary branch vector cache that maintains metadata for conditional branch instructions, allowing for selective streaming of micro-operations based on prediction outcomes, thereby preventing cache line invalidation due to mispredictions and optimizing cache utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional micro-operations cache is used for conditional branch instructions, then cache structure is simple, but cache lines are invalidated on misprediction causing increased power consumption and latency
Solution Approach 1:
The micro-operations cache is segmented into multiple independent cache lines, each capable of holding different micro-operations sequences. When a branch misprediction occurs, only the specific cache line containing the mispredicted branch is invalidated, rather than the entire cache. This segmentation allows the cache to maintain simplicity while reducing the impact of mispredictions on power consumption and performance.
Solution Approach 2:
The cache system dynamically adjusts its behavior based on branch prediction outcomes. The branch predictor dynamically updates predictions, and the cache dynamically invalidates or retains specific cache lines based on whether mispredictions occur. This dynamic approach allows the system to optimize power consumption by avoiding unnecessary cache invalidations while maintaining the ability to handle complex branching patterns.
2Reliability
If cache lines are invalidated on branch misprediction, then correct execution flow is restored, but latency increases due to cache refill
Solution Approach 1:
The cache invalidation mechanism applies local quality by selectively invalidating only the specific cache line containing the mispredicted branch instruction, rather than invalidating the entire cache. This localized approach ensures execution accuracy is restored for the mispredicted path while preserving other valid cache lines, thereby minimizing latency caused by cache refills.
Solution Approach 2:
The system performs preliminary actions by pre-fetching and storing multiple possible execution paths in the micro-operations cache before misprediction occurs. When a misprediction is detected, the correct path is already available in the cache, reducing the latency associated with cache refill and allowing faster recovery from mispredictions.
3Productivity
If micro-operations are streamed to execution unit without termination control, then throughput is maintained, but energy is wasted on executing micro-operations after branch completion
Solution Approach 1:
The system implements feedback control by monitoring the execution status of micro-operations and using branch prediction outcomes to dynamically control the streaming process. When a branch is predicted to be taken or not taken, this feedback information is used to terminate the streaming of micro-operations appropriately, preventing energy waste on unnecessary executions while maintaining high throughput for valid execution paths.
Solution Approach 2:
The system applies partial action by streaming only the necessary portion of micro-operations to the execution unit based on branch prediction outcomes. Instead of streaming all micro-operations regardless of branch status, the system streams only those micro-operations that are relevant to the predicted execution path, thereby reducing energy consumption while maintaining throughput efficiency.
Data Source
AI summary
Various example embodiments for supporting processor capabilities are presented herein. Various example embodiments for supporting processor capabilities may be configured to support increased efficiency in utilization of a micro-operations cache (UC) of a processor. Various example embodiments for supporting increased efficiency in utilization of a UC of a processor may be configured to support increased efficiency in utilization of the UC of the processor based on configuration of the processor such that UC lines created by a prediction window (PW) during execution of a set of instructions by the processor are not invalidated on misprediction of a branch instruction in the set of instructions.