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Auxiliary Processor Instruction for Page Table Look-ups

IP.com Disclosure Number: IPCOM000013142D
Original Publication Date: 2003-Jun-16
Included in the Prior Art Database: 2003-Jun-16
Document File: 1 page(s) / 42K

Publishing Venue

IBM

Abstract

To provide maximum flexibility and reduce hardware complexity some microprocessors invoke operating system firmware to perform page table look-up operations. While an all firmware solution provides great flexibility, it can utilize a large amount of processor bandwidth. Described is an instruction that pushes some of the page table management into the Auxiliary Processor Unit (APU) or application specific part of the processor hardware where it can provide a generic solution or a more specific solution with input from the operating system design, while still maintaining some of the performance benefit of using hardware to perform the page table look-up.

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Auxiliary Processor Instruction for Page Table Look-ups

  Disclosed is an instruction for assisting page table look-ups which can be inserted into a main microprocessor instruction stream and be interpreted by an Auxiliary Processor Unit (APU). To provide maximum flexibility and reduce hardware complexity some microprocessors, such as the PowerPC* 4XX processor family, invoke operating system firmware to perform page table look-up operations. Using firmware to perform page table look-ups can drive a significant amount of processor utilization though. The flexibility of a firmware driven look-up can be maintained with a reduced performance penalty by off loading some of the more data intensive operations of the page table look-up to an APU.

    A set of registers is provided to describe the page table, its entries, organization and in some cases knowledge of the hash algorithm in a way that the hardware can perform either a search or direct look-up of the page table. Characteristics of the page table typically needed are the base address of the page table, the size of the page table, the size of a page table entry grouping (PTEG), the size of a page table entry (PTE), and the offset of the compare field within the PTE. Additional registers can be added to control the type of look-up performed or for more operating system specific, and complex look-ups.

    When a page table look-up is required, the operating system firmware is invoked and typically is provided the address n...