Cache Way Subset Preparation for Power and Latency Trade-offs
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Solution Overview
Problem
Processor caches face high power consumption due to maintaining storage elements in an accessible state, which increases access latency as transitioning them takes time.
Innovation Solution
The processor prepares only a subset of cache ways for access based on predicted usage, using an address generation unit, way predictor, and partial set predictor to determine and precharge the necessary ways before final access determination, reducing unnecessary power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If storage elements are maintained in an accessible state, then access speed is improved, but power consumption increases
Solution Approach 1:
The patent applies preliminary action by precharging bitlines of cache ways in advance of actual data access. The system predicts which cache ways will be needed and prepares them beforehand, so when access is required, the storage elements are already in the accessible state without waiting for last-minute transitions. This resolves the contradiction by preparing the accessible state proactively rather than maintaining it continuously.
Solution Approach 2:
The patent implements dynamics by making the cache way preparation state changeable and adaptive. Instead of a static all-or-nothing approach, the system dynamically determines which specific cache ways need preparation based on access patterns and predictions. The controller adjusts the preparation state of individual ways rather than treating the entire cache uniformly, optimizing both power consumption and access speed dynamically.
2Reliability
If all cache ways are prepared for access, then access reliability is improved, but power consumption increases
Solution Approach 1:
The patent applies segmentation by dividing the cache into individual ways and preparing only the necessary subset rather than the entire cache. The controller identifies which specific ways contain the needed data and prepares only those ways, segmenting the preparation operation to avoid unnecessary power consumption in unused cache regions while maintaining reliability for the accessed data.
Solution Approach 2:
The patent implements partial action by preparing only the necessary subset of cache ways rather than all ways. The system uses predictions and address components to determine the minimal set of ways that need preparation, avoiding excessive preparation of ways that won't be accessed. This partial approach maintains sufficient reliability for actual access needs while significantly reducing power consumption compared to preparing the entire cache.
3Use of energy by moving object
If storage elements are transitioned to accessible state on demand, then power consumption is reduced, but access latency increases
Solution Approach 1:
The patent resolves this contradiction through preliminary action by precharging bitlines of predicted cache ways before actual data access occurs. The system uses address components and predictions to identify which ways will be needed and prepares them in advance during idle or low-priority time slots, eliminating the delay that would otherwise occur when transitioning storage elements to the accessible state at the moment of access.
Solution Approach 2:
The patent implements continuity of useful action by overlapping the preparation process with other cache operations or idle periods. Instead of waiting for a separate preparation phase, the system continues useful actions (such as precharging bitlines) during the time when other cache ways are being accessed or when the processor is idle, making the preparation time invisible to the overall access timeline and maintaining continuous productive activity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces power consumption and access latency by preparing only the required cache ways for access, thereby conserving energy and improving processing efficiency.
Implementation Method 1
precharging the bitlines for the cache way that stores a tag identifier
Data Source
AI summary
For a memory access at a processor, only a subset (less than all) of the ways of a cache associated with a memory address is prepared for access. The subset of ways is selected based on stored information indicating, for each memory access, which corresponding way of the cache was accessed. The subset of ways is selected and preparation of the subset of ways is initiated prior to the final determination as to which individual cache way in the subset is to be accessed.