Per-Thread TLB Flush Tracking for Power-Efficient Processor Wakeups
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Solution Overview
Problem
Current computing systems waste power by issuing TLB Shootdown interrupts to processors that have already flushed their TLB information, causing unnecessary wake-ups from low-power states during memory re-allocation, leading to increased overall power consumption.
Innovation Solution
Implementing a mechanism where the OS tracks TLB flushes on a per-thread basis using a special register space to identify processors that have already flushed their TLB information, preventing unnecessary TLB Shootdown interrupts and allowing processors to remain in a sleep state longer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the OS issues TLB Shootdown interrupts to all processors during memory re-allocation, then TLB consistency is maintained, but power consumption increases due to unnecessary processor wake-ups
Solution Approach 1:
The patent segments the processor set into two groups: processors that have flushed their TLBs (and don't need interrupts) and processors that haven't flushed (and do need interrupts). This segmentation is achieved through per-thread TLB flush tracking, allowing the OS to selectively issue interrupts only to the necessary subset of processors, thereby maintaining TLB consistency while reducing unnecessary wake-ups and power consumption.
Solution Approach 2:
The patent implements a feedback mechanism where processors report their TLB flush status to the OS through a tracking data structure. This feedback allows the OS to make informed decisions about which processors need TLB Shootdown interrupts, enabling selective interrupt issuance that maintains consistency while minimizing power consumption from unnecessary wake-ups.
2Loss of energy
If the OS tracks TLB flushes on a per-thread basis using register space, then unnecessary interrupts are prevented, but device complexity increases
Solution Approach 1:
The patent implements self-service by having processors automatically update their own TLB flush status in the tracking data structure when they flush their TLBs. This self-updating mechanism eliminates the need for complex centralized tracking logic, reducing overall system complexity while still enabling the OS to identify which processors need interrupts and prevent unnecessary wake-ups.
3Use of energy by moving object
If processors remain in sleep state longer, then power consumption decreases, but response time to legitimate interrupts increases
Solution Approach 1:
The patent applies preliminary action by having processors flush their TLBs and update their flush status before entering sleep states. This preliminary flushing ensures that when processors wake up, they are ready to handle legitimate TLB-related interrupts immediately, maintaining fast response times for necessary interrupts while allowing longer sleep durations to reduce overall power consumption.
Data Source
AI summary
A method is described that includes recognizing that TLB information of one or more hardware threads is to be invalidated. The method also includes determining which ones of the one or more hardware threads are in a state in which TLB information is flushed. The method also includes directing a TLB shootdown to those of the or more hardware threads that are in a state in which TLB information is not flushed.