TLB Valid Bits for Multi-Page Size Probing
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Solution Overview
Problem
Current translation lookaside buffers (TLBs) face challenges in supporting multiple page sizes efficiently, leading to high TLB miss rates and performance issues due to limitations in caching virtual to physical mappings, especially when applications access memory with varied page sizes.
Innovation Solution
The implementation of a TLB with multiple valid bits and reconfigurable sub-TLBs allows for probing multiple page sizes in a single probe cycle, combined with coalescing using a narrow-adder to reduce carry propagation overhead, enabling flexible page size allocation and efficient mapping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a TLB stores only a small subset of page table mappings for quick access, then translation speed is improved, but TLB miss rate increases when applications access memory with varied page sizes
Solution Approach 1:
The TLB is divided into multiple sub-TLBs, each capable of storing mappings for different page sizes. This segmentation allows the system to maintain multiple specialized caches simultaneously, improving the overall hit rate for varied page size access patterns while preserving quick access speeds within each sub-TLB.
Solution Approach 2:
The sub-TLBs are reconfigurable, allowing dynamic adjustment of their capacity and page size support based on application requirements. This dynamic reconfiguration enables the TLB to adapt to different workload characteristics, maintaining high hit rates across diverse memory access patterns without sacrificing translation speed.
2Adaptability or versatility
If the TLB probes for multiple page sizes sequentially, then comprehensive page size support is achieved, but probe time increases
Solution Approach 1:
Multiple page size probes are merged into a single simultaneous probe operation. The control circuit generates probe signals for multiple page sizes at the same time and uses bitwise OR logic to combine the results, achieving comprehensive page size support without increasing probe time beyond a single cycle.
Solution Approach 2:
The probe circuit is designed to handle multiple page sizes through a universal probing mechanism. By using valid bit masks and bitwise OR operations, the same probe infrastructure serves multiple page size functions simultaneously, eliminating the need for separate sequential probe sequences for each page size.
3Adaptability or versatility
If the TLB is reconfigured to support different page sizes, then adaptability to application patterns is improved, but device complexity increases
Solution Approach 1:
Different sub-TLBs are configured with different capacities and page size characteristics optimized for specific access patterns. This local quality approach allows each sub-TLB to be specialized for its intended workload while maintaining overall system adaptability, without requiring the entire TLB structure to be maximally complex.
Solution Approach 2:
The TLB configuration is changed by adjusting parameters such as sub-TLB capacity and valid bit patterns rather than fundamentally restructuring the hardware. This parameter-based reconfiguration achieves high adaptability through software-controlled settings while keeping the underlying device structure relatively simple and manageable.
4Reliability
If coalescing is implemented using traditional adders, then carry propagation is handled correctly, but overhead in terms of physical size and power usage increases
Solution Approach 1:
The carry propagation function is extracted from the main coalescing operation and handled separately. By detecting carry conditions and adjusting valid bits accordingly, the patent removes the need for full-width adders with complete carry propagation chains, significantly reducing the physical size and power consumption of the coalescing logic while maintaining correctness.
Data Source
AI summary
A processor includes a translation lookaside buffer (TLB) to store a TLB entry, wherein the TLB entry comprises a first set of valid bits to identify if the first TLB entry corresponds to a virtual address from a memory access request, wherein the valid bits are set based on a first page size associated with the TLB entry from a first set of different page sizes assigned to a first probe group; and a control circuit to probe the TLB for each page size of the first set of different page sizes assigned to the first probe group in a single probe cycle to determine if the TLB entry corresponds to the virtual address from the memory access request.