Variable Page Size TLB Entry Allocation for Translation Latency
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Solution Overview
Problem
The existing virtual memory translation mechanisms, relying on page tables and translation lookaside buffers (TLBs), face inefficiencies due to the slow lookup times in page tables and limited size constraints of TLBs, leading to suboptimal performance in address translations.
Innovation Solution
Implementing a variable page size TLB system that allocates entries based on detected misses, specifying a default page size for requests and reissuing them with the actual page size when necessary, allowing for efficient consolidation of overlapping requests and reduced reliance on larger L2 TLBs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a TLB is limited in size to fit integrated circuit area constraints, then device area is reduced, but translation speed and efficiency deteriorate due to limited cache capacity
Solution Approach 1:
The patent implements a variable page size TLB where the default page size is dynamically selected based on the client type making the request. Different clients (e.g., CPU, GPU, I/O devices) have different default page sizes configured in their respective configuration registers. This dynamic adaptation allows the TLB to optimize for the specific access patterns of each client, improving translation efficiency without increasing TLB area.
2Reliability
If page tables are used for address translation, then complete translation coverage is achieved, but translation speed deteriorates due to slow lookup operations
Solution Approach 1:
The patent pre-loads frequently used address translations into the TLB cache before they are actually needed. By anticipating which translations will be required and loading them in advance, the system reduces the need for slow page table lookups during actual memory access operations, thereby improving translation speed while maintaining complete translation coverage.
3Measurement precision
If overlapping requests are processed individually, then request accuracy is maintained, but bandwidth usage increases and performance decreases
Solution Approach 1:
The patent consolidates multiple overlapping translation requests into a single TLB lookup operation. When multiple requests target overlapping address ranges, the system merges them and performs one unified lookup, retrieving all necessary translations in a single operation. This approach maintains accurate translation results while significantly reducing the bandwidth consumption associated with multiple separate lookup operations.
Data Source
AI summary
Systems, apparatuses, and methods for selecting default page sizes in a variable page size translation lookaside buffer (TLB) are disclosed. In one embodiment, a system includes at least one processor, a memory subsystem, and a first TLB. The first TLB is configured to allocate a first entry for a first request responsive to detecting a miss for the first request in the first TLB. Prior to determining a page size targeted by the first request, the first TLB specifies, in the first entry, that the first request targets a page of a first page size. Responsive to determining that the first request actually targets a second page size, the first TLB reissues the first request with an indication that the first request targets the second page size. On the reissue, the first TLB allocates a second entry and specifies the second page size for the first request.