Virtual Aliasing Cache Hit Miss Detector for VIVT Caches
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Solution Overview
Problem
Virtually-indexed virtually-tagged (VIVT) caches face issues with virtual aliased addresses, leading to false cache misses and data incoherency, which result in performance penalties and incorrect data retrieval due to the inability to correctly distinguish between true and false misses.
Innovation Solution
A virtual aliasing cache hit/miss detector is introduced, utilizing a translation lookaside buffer (TLB) to translate virtual addresses into physical addresses and a comparator to generate an aliased cache hit/miss indicator, thereby accurately determining cache hits and misses even in the presence of aliased addresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a virtually-indexed virtually-tagged cache is used to achieve faster cache access times, then cache access speed is improved, but false cache misses occur due to virtual aliased addresses
Solution Approach 1:
A translation lookaside buffer (TLB) is introduced as an intermediary component between the VIVT cache and the alias detection logic. The TLB stores virtual-to-physical address translations and provides them to the alias detector, enabling accurate distinction between true and false aliases without slowing down the cache access path.
Solution Approach 2:
The cache system is segmented into multiple functional components: the VIVT cache for fast access, a separate alias detector for accuracy, and a TLB for address translation. This segmentation allows each component to perform its specialized function efficiently, with the alias detector operating in parallel to determine cache hit/miss status.
2Device complexity
If virtual aliased addresses are not distinguished, then cache access remains simple, but data incoherency occurs due to false cache misses
Solution Approach 1:
The alias detector performs preliminary detection of virtual aliases before the cache access is finalized. By detecting potential false aliases in advance and using the TLB to verify physical address equivalence, the system prevents data incoherency from occurring, ensuring stable data composition.
Solution Approach 2:
The alias detector provides feedback about the presence of virtual aliases to the cache control logic. When aliases are detected, the system uses TLB translations to determine whether they are false aliases, and adjusts the cache hit/miss determination accordingly, maintaining data coherency through feedback-based control.
3Productivity
If false cache misses are generated by virtual aliased addresses, then performance penalties occur due to unnecessary secondary cache or main memory access, but the root cause is the inability to distinguish aliased addresses
Solution Approach 1:
The alias detector operates in parallel with the cache access to preliminarily determine whether a virtual alias is present. By detecting false aliases before the cache miss is finalized, the system prevents unnecessary secondary cache or main memory accesses, recovering the time that would have been lost.
Solution Approach 2:
The alias detector provides feedback about detected virtual aliases to the cache control logic. When false aliases are detected through TLB verification, the system corrects the cache hit/miss status, preventing performance penalties from unnecessary memory accesses and improving overall productivity.
Data Source
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AI summary
Apparatuses and related systems and methods for determining cache hit/miss of aliased addresses in virtually-tagged cache(s) are disclosed. In one embodiment, a virtual aliasing cache hit/miss detector for a VIVT cache is provided. The detector comprises a TLB configured to receive a first virtual address and a second virtual address from the VIVT cache resulting from an indexed read into the VIVT cache based on the first virtual address. The TLB is further configured to generate first and second physical addresses translated from the first and second virtual addresses, respectively. The detector further comprises a comparator configured to receive the first and second physical addresses and effectuate a generation of an aliased cache hit/miss indicator based on a comparison of the first and second physical addresses. In this manner, the virtual aliasing cache hit/miss detector correctly generates cache hits and cache misses, even in the presence of aliased addressing.