Counter-Based Invalidation for Metadata Previous Write Queue
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Solution Overview
Problem
The presence of duplicate metadata entries in a metadata store can reduce the overall performance of a microprocessor, as it becomes time-consuming and power-consuming to search for existing entries before writing new ones, and a previous write queue (PWQ) may incorrectly block new entries from being written due to false matches.
Innovation Solution
Implementing a counter-based entry invalidation system for the metadata PWQ, where a counter is initialized and incremented for each operation, and entries are invalidated when the counter reaches a threshold, ensuring that valid tags are set to prevent incorrect blocking and allow new entries to overwrite invalid ones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a previous write queue (PWQ) is used to track metadata entries, then duplicate entries are prevented, but false matches cause incorrect blocking of new entries
Solution Approach 1:
A counter is introduced as an intermediary element between the PWQ and the metadata store. The counter tracks the number of operations since an entry was written to the PWQ, and when it reaches a threshold, the entry is invalidated. This intermediary mechanism resolves the false match problem by providing temporal context to PWQ entries, allowing new entries to overwrite invalidated PWQ entries without incorrect blocking.
2Reliability
If metadata entries are searched in the metadata store before writing, then duplicate entries are detected, but the search process is time-consuming and power-consuming
Solution Approach 1:
The search function is extracted from the metadata store and relocated to the PWQ. Instead of searching the entire metadata store for duplicates, the system only checks the PWQ, which contains a limited subset of recent entries. This extraction dramatically reduces search time and power consumption while maintaining reliability in detecting duplicates.
Solution Approach 2:
Entries are pre-loaded into the PWQ before being written to the metadata store. This preliminary action creates a staging area where duplicate detection can occur efficiently using the counter-based invalidation mechanism, avoiding the need for time-consuming searches in the full metadata store.
3Reliability
If PWQ entries are retained indefinitely, then duplicate detection accuracy is maintained, but memory resources are wasted on invalid entries
Solution Approach 1:
The PWQ entries are invalidated periodically based on a counter that reaches a threshold after a certain number of operations. This periodic invalidation mechanism ensures that old, potentially invalid entries are removed from the PWQ, freeing up memory resources while maintaining duplicate detection accuracy for recent entries.
Data Source
AI summary
Embodiments of the invention relate to counter-based entry invalidation for a metadata previous write queue (PWQ). An aspect of the invention includes writing an address into an entry in the metadata PWQ, the address being associated with an instance of metadata received from a pipeline and setting a valid tag associated with the entry in the metadata PWQ to valid. Another aspect of the invention includes initializing a counter to zero and incrementing the counter based on receiving a count signal from the pipeline until the counter is equal to a threshold. Yet another aspect of the invention includes setting the valid tag to invalid based on the counter being equal to the threshold.