Fabric Control Circuit Dynamic Source Throttling
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Solution Overview
Problem
Modern communication fabrics in processors face bandwidth degradation due to excessive re-ordering of ownership responses, leading to head-of-line blocking and throughput degradation under varying and unpredictable request loads.
Innovation Solution
A dynamic source throttling mechanism that uses statistics to control the injection rate of requests, implementing an implicit hysteresis closed loop to manage fabric throughput and maintain optimal head-of-line blocking, thereby adjusting the injection rate based on fabric load changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the fabric receives requests from a large number of sources with varying and unpredictable levels, then the fabric can handle diverse workloads, but the fabric becomes overwhelmed and experiences excessive re-ordering of ownership responses
Solution Approach 1:
The patent implements a feedback mechanism where the fabric monitors ownership response re-ordering metrics and dynamically adjusts request injection rates from sources. When excessive re-ordering is detected, the fabric provides feedback to throttle source request rates, preventing fabric overload and maintaining optimal throughput while handling diverse workloads.
Solution Approach 2:
The system dynamically adjusts the injection rate of requests from sources based on fabric load conditions. The fabric transitions from a static request acceptance model to a dynamic one where request rates are continuously adapted according to current fabric utilization and re-ordering metrics, enabling optimal performance across varying workload conditions.
2Productivity
If ownership requests are sent out concurrently to achieve throughput, then pipelining efficiency is improved, but head-of-line blocking occurs due to re-ordering requirements
Solution Approach 1:
The system uses feedback from ownership response arrival patterns to dynamically control the concurrency of outstanding ownership requests. When re-ordering causes head-of-line blocking, the fabric provides feedback to reduce the number of concurrent requests, thereby eliminating blocking while maintaining optimal pipelining efficiency through adaptive request issuance.
3Power
If the fabric operates with high bandwidth scaling and distributed architecture, then system capacity is increased, but the fabric is increasingly stressed causing excessive re-ordering
Solution Approach 1:
The patent applies partial action by throttling source request rates to optimal levels rather than allowing maximum request issuance. Even though the fabric has high bandwidth capacity, not all capacity can be effectively utilized due to re-ordering constraints. The system issues only the optimal number of concurrent requests that maximize throughput without causing excessive re-ordering, leaving some potential bandwidth unused but achieving better effective throughput.
Data Source
AI summary
In one embodiment, a fabric circuit is to receive requests for ownership and data commits from an agent. The fabric circuit includes a control circuit to maintain statistics regarding the requests for ownership and the data commits and throttle the fabric circuit based at least in part on the statistics. Other embodiments are described and claimed.