Processor Circuit Load-Use Stall Reduction via Data Buffering
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Solution Overview
Problem
In CPU architectures, load-use stalls occur due to cache access delays when multiple load instructions use the same register, leading to performance degradation in superscalar processing.
Innovation Solution
A processor circuit and method that includes an instruction decode unit, detector, address generator, and data buffer to detect when load instructions use the same register, preloading data into the buffer to avoid cache access delays, thereby reducing pipeline stalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the CPU uses a cache mechanism to access data, then the access time is reduced, but load-use stalls still occur when data is requested by a load instruction just received
Solution Approach 1:
The processor detects multiple load instructions targeting the same register and preloads the data for the first load instruction into a data buffer before the cache access is complete. This preliminary action allows subsequent manipulation instructions to execute immediately using the preloaded data, eliminating load-use stalls and maintaining high instruction throughput while preserving fast cache access.
2Productivity
If the CPU uses superscalar architecture to issue multiple instructions per clock cycle, then throughput is increased, but load-use stalls degrade performance when multiple load instructions use the same register
Solution Approach 1:
A data buffer is introduced as an intermediary between the cache memory and the execution units. When multiple load instructions target the same register, the buffer stores the loaded data and makes it immediately available to subsequent manipulation instructions, decoupling the cache access latency from the instruction execution pipeline and maintaining superscalar throughput.
Solution Approach 2:
The processor performs preliminary detection of load instructions targeting the same register and preloads data into the buffer before the cache operation completes. This allows the superscalar pipeline to continue issuing and executing manipulation instructions without stalling, preserving high instruction throughput despite cache access delays.
3Reliability
If the processor waits for cache access to complete before executing manipulation instructions, then data correctness is ensured, but pipeline stalls increase
Solution Approach 1:
The processor detects multiple load instructions to the same register and preloads the data for the first load instruction into a data buffer before the cache access completes. This preliminary action ensures data correctness is maintained while allowing manipulation instructions to execute immediately, eliminating pipeline stalls and improving overall pipeline efficiency.
Data Source
AI summary
A processor circuit includes an instruction decode unit, an instruction detector, an address generator and a data buffer. The instruction decode unit is configured to decode a first load instruction included in a plurality of load instructions to generate a first decoding result. The instruction detector, coupled to the instruction decode unit, is configured to detect if the load instructions use a same register. The address generator, coupled to the instruction decode unit, is configured to generate a first address requested by the first load instruction according to the first decoding result. The data buffer is coupled to the instruction detector and the address generator. When the instruction detector detects that the load instructions use the same register, the data buffer is configured to store the first address generated from the address generator, and store data requested by the first load instruction according to the first address.