Adaptive Snooping Control for Multi-Core Processor Bus Latency
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Solution Overview
Problem
In multi-core processor chips, the increasing number of cores leads to longer broadcast times for bus commands and higher power consumption, as well as inefficient use of resources due to blind responses to fastpath commands that cannot be satisfied by caches, wasting directory read bandwidth and consuming unnecessary power.
Innovation Solution
Implementing a method to dynamically enable or disable snooping on a fastpath bus based on statistical data indicating the likelihood of a local cache's ability to provide early data intervention, thereby optimizing bus usage and reducing power consumption by only enabling snooping when the cache can satisfy requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If snooping is enabled for all fastpath commands, then cache coherency is maintained, but power consumption increases and directory read bandwidth is wasted
Solution Approach 1:
The patent dynamically changes the snooping parameter based on statistical analysis of command patterns. The system monitors whether early data intervention is successful over time and adjusts the snooping enablement state accordingly, transforming a static parameter into a dynamic one that adapts to actual workload characteristics
Solution Approach 2:
The system implements feedback by monitoring the success rate of early data intervention attempts and using this information to control future snooping behavior. The statistical data about command satisfaction rates feeds back into the decision logic that determines whether snooping should be enabled or disabled
2Reliability
If snooping is enabled for all fastpath commands, then cache coherency is maintained, but directory read bandwidth is consumed unnecessarily
Solution Approach 1:
Instead of enabling snooping for all fastpath commands (excessive action), the system enables it only for the subset of commands that are likely to benefit based on statistical patterns. This partial action approach applies snooping selectively rather than universally, reducing unnecessary directory reads while maintaining coherency where needed
3Productivity
If the number of core processors is increased, then processing capacity is improved, but bus command broadcast time increases
Solution Approach 1:
The patent extracts critical path operations from the general bus broadcast mechanism by implementing early data intervention on the fastpath. By handling certain commands through this specialized path that bypasses full bus arbitration and broadcast, the system reduces the time impact of having multiple cores while maintaining processing capacity
4Productivity
If the number of core processors is increased, then processing capacity is improved, but power consumption increases
Solution Approach 1:
The system introduces dynamic power management for the snooping function. Rather than having snooping continuously enabled across all cores, the system dynamically adjusts snooping activation based on statistical workloads and cache satisfaction rates, allowing power consumption to adapt to actual processing needs
Data Source
AI summary
Statistical data is used to enable or disable snooping on a bus of a processor. A command is received via a first bus or a second bus communicably coupling processor cores and caches of chiplets on the processor. Cache logic on a chiplet determines whether or not a local cache on the chiplet can satisfy a request for data specified in the command. In response to determining that the local cache can satisfy the request for data, the cache logic updates statistical data maintained on the chiplet. The statistical data indicates a probability that the local cache can satisfy a future request for data. Based at least in part on the statistical data, the cache logic determines whether to enable or disable snooping on the second bus by the local cache.