Contention Tracking for Exclusive Memory Operation Latency
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Solution Overview
Problem
Existing processor cache management systems face performance bottlenecks due to memory contention, leading to increased cache coherence overhead and reduced access speed when multiple threads contend for data access.
Innovation Solution
Implementing a contention tracking mechanism that identifies contentious memory locations and uses this information to manage cache operations, such as storing data in shared or private caches based on contention status, and processing memory operations out-of-order to reduce lock acquisition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple threads access memory locations simultaneously, then processor productivity increases, but cache coherence overhead increases and access speed decreases
Solution Approach 1:
The system performs preliminary actions by tracking contention history and predicting future contention before it occurs. The contention tracker records which memory locations have been contested in the past, and this information is used to pre-configure cache management strategies, such as prioritizing certain cache lines or preparing lock acquisition sequences, thereby reducing coherence overhead when actual contention happens.
Solution Approach 2:
The contention tracking mechanism provides feedback about which memory locations are frequently contested. This feedback is used to dynamically adjust cache management policies, such as promoting frequently contested locations to higher cache tiers or adjusting eviction strategies, thereby optimizing the balance between productivity and cache coherence maintenance.
2Reliability
If threads wait for lock acquisition, then data access safety is ensured, but access time increases
Solution Approach 1:
The system performs preliminary lock acquisition attempts for threads that will need to access contentious memory locations. By predicting which locations are likely to be contested based on historical data, the system can pre-acquire locks or prepare thread contexts, reducing the waiting time when actual data access is needed while still ensuring safety through proper locking mechanisms.
Solution Approach 2:
The lock acquisition strategy becomes dynamic based on contention patterns. The system adjusts lock acquisition timing and strategy according to real-time and historical contention data, allowing threads to acquire locks earlier or use different acquisition sequences for frequently contested locations versus those that are less contested, thereby optimizing both safety and time.
3Speed
If cache stores multiple copies of data, then access speed increases, but cache coherence management complexity increases
Solution Approach 1:
The system applies local quality by treating different cache lines differently based on their contention characteristics. Frequently contested memory locations are managed with stricter coherence policies and prioritized in certain cache regions, while less contested locations use more relaxed policies. This localized differentiation maintains fast access for critical data while reducing overall coherence management complexity.
Solution Approach 2:
The cache management system changes parameters such as cache line priority, eviction thresholds, and coherence check frequencies based on contention history. By adjusting these parameters dynamically for different memory locations, the system optimizes access speed for high-performance needs while managing coherence complexity through data-driven parameter adaptation rather than uniform strict policies.
Data Source
AI summary
The technology disclosed herein involves tracking contention and using the tracked contention to reduce latency of exclusive memory operations. The technology enables a processor to track which locations in main memory are contentious and to modify the order exclusive memory operations are processed based on the contentiousness. A thread can include multiple exclusive operations for the same memory location (e.g., exclusive load and a complementary exclusive store). The multiple exclusive memory operations can be added to a queue and include one or more intervening operations between them in the queue. The processor may process the operations in the queue based on the order they were added and may use the tracked contention to perform out-of-order processing for some of the exclusive operations. For example, the processor can execute the exclusive load operation and because the corresponding location is contentious can process the complementary exclusive store operation before the intervening operations.