Hot Cache Line Arbitration in SMP Systems
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Solution Overview
Problem
In symmetric multiprocessing (SMP) systems, the traditional bias towards remote cache line requests over local requests leads to excessive transmission of 'hot cache lines', causing system-wide starvation and increased latency, especially as the number of processors grows, resulting in delayed access to shared resources.
Innovation Solution
Implementing a hot cache line arbitration method that detects and tracks requests, servicing them within local clusters before allowing remote access, ensuring each local requestor acquires exclusive access before remote requestors, thereby reducing unnecessary cache line transfers and improving lock efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If remote cache line requests are prioritized over local requests, then remote access fairness is improved, but system-wide starvation and latency increase
Solution Approach 1:
The patent segments the arbitration process into two distinct phases: a local arbitration phase where local requests are serviced first, and a remote arbitration phase where remote requests are serviced. This segmentation allows the system to prioritize local requests without completely blocking remote access, thereby resolving the contradiction between remote fairness and system-wide latency.
Solution Approach 2:
The patent implements preliminary action by servicing local cache line requests before remote requests in the arbitration hierarchy. This preliminary servicing of local requests prevents system-wide starvation and reduces latency, while still allowing remote requests to be fulfilled afterward, thus maintaining remote access fairness.
2Adaptability or versatility
If hot cache lines are transmitted across drawers and clusters, then remote processors can access shared resources, but transmission latency increases
Solution Approach 1:
The patent segments cache line access into local drawer/cluster access and remote access phases. By arbitrating local requests first within the drawer and cluster before allowing remote access, the system reduces unnecessary long-distance transmissions of hot cache lines, thereby reducing transmission latency while still enabling remote resource access when necessary.
Solution Approach 2:
The patent applies local quality by giving priority to local requests within the same drawer and cluster before allowing remote requests. This localized arbitration reduces the need for hot cache lines to be transmitted across drawers and clusters, thereby reducing transmission latency while maintaining remote access capability.
3Adaptability or versatility
If traditional arbitration favors remote requests, then remote processor fairness is improved, but local processors experience starvation
Solution Approach 1:
The patent segments the arbitration process into local and remote phases, where local requests are arbitrated and serviced first within their drawer and cluster, and only after local requests are handled does the system service remote requests. This segmentation ensures local processors do not experience starvation while still providing fairness to remote processors.
Solution Approach 2:
The patent implements preliminary action by servicing local cache line requests before remote requests. This preliminary servicing ensures local processors maintain productivity and do not experience starvation, while remote processors still receive fair access to shared resources afterward, thus resolving the contradiction between remote fairness and local efficiency.
Data Source
AI summary
Embodiments of the present invention are directed to hot cache line arbitration. An example of a computer-implemented method for hot cache line arbitration includes detecting, by a processing device, a hot cache line scenario. The computer-implemented method further includes tracking, by the processing device, hot cache line requests from requesters to determine subsequent satisfaction of the requests. The computer-implemented method further includes facilitating, by the processing device, servicing of the requests according to hierarchy of the requestors.