Processor Context Identifier Renaming for TLB Area Reduction
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Solution Overview
Problem
As processors increase in performance capability, the number of bits used to define address-space identifiers (ASIDs) and virtual machine identifiers (VMIDs) grows, leading to larger translation lookaside buffer (TLB) tag arrays, which occupy more die area and consume more power.
Innovation Solution
A context identification circuit is configured to receive context identifiers and assign rename values with fewer bits, which are then used by a TLB circuit to cache translations. This approach reduces the size of TLB tag storage, saving die area and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of bits used to define ASID and VMID increases to support more contexts, then the processor can support more applications and virtual machines, but the TLB tag array size increases, occupying more die area and consuming more power
Solution Approach 1:
The context identifier is segmented into two parts: a rename field (subset of bits) stored in the TLB tag array, and a full context identifier stored separately in the TLB data field. This segmentation allows the TLB to support multiple contexts using only a portion of the identifier bits in the tag array, reducing die area while maintaining the ability to distinguish between different applications and virtual machines.
Solution Approach 2:
The patent moves part of the context identification information from the traditional tag array dimension to the data field dimension. Instead of storing the full context identifier in the tag array, the system stores a compressed rename field in the tag and the complete context identifier in the data portion, effectively utilizing a different dimensional space for storage.
2Adaptability or versatility
If the number of bits used to define ASID and VMID increases, then the processor can support more applications and virtual machines, but power consumption increases
Solution Approach 1:
By segmenting the context identifier into a compressed rename field for tagging and a full identifier stored in the data field, the system reduces the number of bits that need to be accessed and compared in the power-consuming tag array, thereby reducing overall TLB power consumption while maintaining support for multiple contexts.
Solution Approach 2:
The patent changes the parameter of context identifier representation from full-width to compressed width in the tag array. By using a rename field with fewer bits than the full context identifier, the system reduces the electrical activity and power consumption associated with tag array operations while preserving the ability to identify multiple contexts.
3Adaptability or versatility
If the TLB tag array size increases to accommodate more context identifiers, then more applications can be supported, but die area increases
Solution Approach 1:
The patent segments the context identifier storage into two locations: a compressed rename field in the tag array and the full context identifier in the data field. This allows the tag array to use fewer bits per entry, reducing the overall TLB circuit area while maintaining the capability to support a large number of applications through the full context identifier stored in the data portion.
Solution Approach 2:
The system creates a compressed copy (rename field) of the context identifier for storage in the tag array, while the full context identifier is stored in the data field. This copying approach allows the tag array to be smaller while still maintaining the ability to uniquely identify multiple applications through the complete identifier available in the data portion.
Data Source
AI summary
An apparatus includes a context identification circuit and a translation lookaside buffer (TLB) circuit. The context identification circuit may be configured to receive a context identifier assigned to a process being executed by a processor, and to assign a rename value to the context identifier that has fewer bits than the context identifier. The TLB circuit may be configured to receive a translation request for a virtual address that is associated with the process. The TLB circuit may be further configured to cache a translation of the virtual address to a corresponding physical address. The given entry may be tagged with a portion of the virtual address and the rename value. In response to a subsequent translation request for the virtual address, the TLB circuit may detect, using the portion of the virtual address and the rename value, a hit on the given entry of the TLB circuit.