Branch Target Buffer Addressing for Pipeline Stall Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing data processing systems face performance degradation due to pipeline stalls and increased memory access when transitioning between differing high-order address bits, and compression methods for address values reduce available address ranges, limiting system effectiveness.
Innovation Solution
A branch target buffer (BTB) system that efficiently compresses branch target addresses by using a shared higher order target portion and multiple unshared lower order target portions, with control fields indicating branch validity and prediction, allowing for the generation of non-speculative target addresses for short, medium, and long branches, reducing the need for full target address storage and minimizing speculative address generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If compression methods are used to reduce address value size, then the size of communication buses and memory storage is reduced, but the available address range is significantly reduced
Solution Approach 1:
The address value is segmented into high-order bits and low-order bits. The high-order bits are compressed and stored in a table, while the low-order bits are stored directly. This segmentation allows the address range to be extended beyond the compression limit by combining the compressed high-order portion with the uncompressed low-order portion.
Solution Approach 2:
A table structure is introduced as an intermediary between the compressed high-order address bits and the full address reconstruction. The table stores the relationship between compressed high-order bits and their corresponding full high-order address values, enabling the system to overcome the address range limitation of compression methods.
2Quantity of substance
If pipeline stalls occur when transitioning between differing high order bits, then address compression is achieved, but system performance is degraded
Solution Approach 1:
The high-order address bits are pre-compressed and the results are stored in a table during system initialization or when address patterns are detected. This preliminary compression allows the pipeline to avoid stalls during address transitions, as the compressed values are already prepared and can be quickly retrieved when needed.
Solution Approach 2:
The system monitors address transition patterns and adjusts the compression strategy based on detected patterns. When transitions between differing high-order bits are detected, the system can switch between compressed and uncompressed address modes, providing feedback-based optimization that maintains performance while achieving compression where beneficial.
3Adaptability or versatility
If more operands are retrieved from main memory rather than cache, then address range is increased, but system performance is degraded
Solution Approach 1:
By segmenting the address into compressed high-order bits and uncompressed low-order bits, the system can maintain a larger effective address range without requiring full uncompressed addresses to be stored in cache. This allows more operands to remain in cache while still supporting extended address ranges.
Solution Approach 2:
The system changes the parameter representation of addresses by using compressed high-order bits combined with uncompressed low-order bits. This parameter transformation allows the system to maintain cache efficiency while supporting larger address ranges, as the compressed representation reduces the memory footprint of address-related data structures.
Data Source
AI summary
A branch target buffer (BTB) receives, from a processor, a current fetch group address which corresponds to a current fetch group including a plurality of instructions. In response to the current fetch group address resulting in a group hit in the BTB, the BTB provides to the processor a branch target address corresponding to a branch instruction within the current fetch group which is indicated by a control field as valid and predicted taken. The BTB generates the branch target address using an unshared lower order target portion, corresponding to the branch instruction and located within the entry of the BTB which caused the group hit, and one of a shared higher order target portion located within the entry of the BTB which caused the group hit or a higher order portion of the current fetch group address based on a value of the control field.