Selective ITLB Access Suppression for Instruction Cache Efficiency
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Solution Overview
Problem
Current computing environments face inefficiencies in instruction fetch processing due to repetitive and unnecessary access to instruction translation lookaside buffers (ITLB) during sequential instruction fetches from the same address page, leading to increased power dissipation and heat generation.
Innovation Solution
A method is introduced to selectively suppress ITLB access for subsequent instruction fetches from the same address page by comparing the results of the most recent ITLB access with the current instruction directory access, generating a suppress signal to avoid repetitive translations and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ITLB access is performed for every instruction fetch, then address translation accuracy is maintained, but power dissipation increases
Solution Approach 1:
The patent performs address translation in advance and buffers the results before they are needed. The ITLB access is performed once per cache line rather than once per instruction, and the translated address is buffered for subsequent instructions from the same cache line, eliminating redundant translation operations while maintaining accuracy.
Solution Approach 2:
The patent applies selective suppression of ITLB access based on local conditions - specifically when multiple instructions are fetched from the same cache line. The suppression logic examines whether the current instruction and previous instructions map to the same cache line, and only suppresses ITLB access when this local condition is met, rather than applying a global suppression policy.
2Productivity
If ITLB access is suppressed for sequential instructions, then processing speed improves, but address translation reliability may deteriorate
Solution Approach 1:
The address translation is performed in advance for the entire cache line before instruction execution begins. The ITLB access occurs once when the cache line is loaded, and the resulting physical address is buffered and reused for all subsequent instructions from that cache line, ensuring both speed and reliability.
Solution Approach 2:
The suppression logic includes feedback mechanisms that monitor whether instructions are indeed from the same cache line. If a branch instruction or cache line boundary is detected, the suppression is lifted and a new ITLB access is performed, ensuring that address translation remains accurate while still providing speedup for sequential instructions.
3Temperature
If ITLB access is performed for each instruction fetch, then address translation freshness is maintained, but heat generation increases
Solution Approach 1:
The patent performs address translation in advance when the cache line is loaded into the instruction cache, rather than performing it repeatedly during instruction fetch. The translated address is stored in a buffer and reused for all instructions from that cache line, reducing heat-generating operations while maintaining translation freshness through buffer invalidation on cache line updates.
4Loss of energy
If ITLB access is selectively suppressed, then power consumption decreases, but device complexity increases
Solution Approach 1:
The suppression logic examines local conditions - specifically whether the current instruction and previous instructions map to the same cache line - and applies suppression only when this local condition is met. This localized approach reduces power consumption for sequential instructions while avoiding the need for complex global suppression mechanisms.
Solution Approach 2:
The instruction cache system performs self-service by maintaining its own address translation information in the IDIR (Instruction Directory). The suppression logic uses information already available in the cache structure (cache line addresses) to determine when suppression is appropriate, rather than requiring additional complex translation management hardware.
Data Source
AI summary
Processing of an instruction fetch from an instruction cache is provided, which includes: determining whether the next instruction fetch is from a same address page as a last instruction fetch from the instruction cache; and based, at least in part, on determining that the next instruction fetch is from the same address page, suppressing for the next instruction fetch an instruction address translation table access, and comparing for an address match results of an instruction directory access for the next instruction fetch with buffered results of a most-recent, instruction address translation table access for a prior instruction fetch from the instruction cache.