TLB Segmentation for Virtual Processing Elements
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Solution Overview
Problem
The use of multithreading and virtualization in modern processors often leads to inefficient resource utilization and performance degradation due to bottlenecks in cache and translation lookaside buffer (TLB) resources.
Innovation Solution
A physical Translation Lookaside Buffer (TLB) is implemented with a combination of content addressable memory having variable page size entries and set associative memory with fixed page size entries, allowing for efficient allocation and sharing of TLB entries among virtual processing elements (VPEs) to optimize memory management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multithreading and virtualization are used to improve hardware resource utilization, then productivity increases, but TLB and cache efficiency deteriorates due to resource contention
Solution Approach 1:
The TLB is segmented into multiple independent sets, where each set is exclusively allocated to a specific virtual processing element (VPE). This segmentation prevents resource contention between VPEs while maintaining high TLB hit rates, as each VPE has dedicated cache lines without interference from other VPEs. The segmentation resolves the contradiction by allowing multiple VPEs to operate simultaneously with guaranteed performance levels.
Solution Approach 2:
The TLB structure is designed to serve multiple functions: it provides dedicated cache lines for each VPE while also supporting shared resources through the second set of entry locations. This multi-functionality allows the same TLB structure to simultaneously improve productivity through virtualization support and maintain reliability through efficient cache utilization for each VPE.
2Device complexity
If a shared TLB structure is used to support multiple VPEs, then device complexity is reduced, but resource utilization efficiency deteriorates due to contention
Solution Approach 1:
Rather than implementing completely separate TLB structures for each VPE (which would increase complexity), the patent segments the TLB into multiple sets that can be independently managed. Each VPE has dedicated access to specific sets, reducing contention while maintaining a unified TLB structure. This segmentation achieves both goals: manageable complexity and high resource utilization efficiency.
Solution Approach 2:
The patent introduces a new dimension of organization by dividing the TLB into multiple sets with different access patterns. Instead of a single shared space, the TLB is organized in a multi-dimensional structure where VPEs can access different sets simultaneously, effectively adding spatial separation without increasing overall structural complexity.
3Reliability
If dedicated TLB entries are allocated to each VPE to improve performance, then TLB hit rate increases, but TLB size requirements increase
Solution Approach 1:
The TLB is divided into multiple sets, with each set containing a portion of the total cache lines. Each VPE is assigned dedicated cache lines within its assigned sets, ensuring high hit rates without requiring each VPE to have access to the entire TLB capacity. This segmentation allows the system to achieve high reliability with a manageable total TLB size.
Solution Approach 2:
Rather than providing every VPE with access to all TLB entries (excessive action), the patent provides each VPE with access to a sufficient subset of entries (partial action) needed for its typical workloads. This partial allocation achieves high hit rates for each VPE while keeping the overall TLB size reasonable.
Data Source
AI summary
Embodiments disclosed pertain to apparatuses, systems, and methods for Translation Lookaside Buffers (TLBs) that support visualization and multi-threading. Disclosed embodiments pertain to a TLB that includes a content addressable memory (CAM) with variable page size entries and a set associative memory with fixed page size entries. The CAM may include: a first set of logically contiguous entry locations, wherein the first set comprises a plurality of subsets, and each subset comprises logically contiguous entry locations for exclusive use of a corresponding virtual processing element (VPE); and a second set of logically contiguous entry locations, distinct from the first set, where the entry locations in the second set may be shared among available VPEs. The set associative memory may comprise a third set of logically contiguous entry locations shared among the available VPEs distinct from the first and second set of entry locations.