Memory Controller Pre-fetch Buffer Management via Status Feedback
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Solution Overview
Problem
Existing techniques for managing pre-fetch data in computing systems are inefficient, leading to wasted system memory bandwidth due to improper timing in storing and purging pre-fetch data, resulting in suboptimal memory performance.
Innovation Solution
A method where a memory controller uses early live status data from a system level cache memory to determine when to purge or hold pre-fetch data in a buffer, allowing it to manage the buffer more efficiently by aligning with the actual needs of read operations, thereby reducing latency and improving memory performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If pre-fetch data is stored in a pre-fetch buffer without using status data, then the memory controller can simplify buffer management, but system memory bandwidth is wasted due to improper timing in storing and purging pre-fetch data
Solution Approach 1:
The memory controller receives status data from the system level cache memory that indicates whether a read operation will be serviced by the system level cache memory or by the pre-fetch buffer. This feedback mechanism allows the memory controller to make informed decisions about when to purge pre-fetch data, preventing bandwidth waste while maintaining appropriate buffer management complexity.
Solution Approach 2:
The memory controller proactively purges pre-fetch data based on status data received from the system level cache memory before the read operation actually occurs. This preliminary action prevents unnecessary data retention that would waste system memory bandwidth, while the controller maintains the ability to hold data when needed.
2Device complexity
If pre-fetch data is purged after a fixed duration of time, then the buffer management is simplified, but the accuracy of pre-fetch operations decreases when the read operation latency varies
Solution Approach 1:
Instead of using a fixed time duration for purging pre-fetch data, the memory controller uses status data feedback from the system level cache memory to determine the appropriate purge timing. This feedback mechanism allows the controller to accurately predict when data should be purged based on actual read operation characteristics, improving pre-fetch accuracy without significantly increasing management complexity.
3Measurement precision
If the memory controller waits for status data from system level cache memory before making purge decisions, then pre-fetch data accuracy is improved, but the time to service read operations increases
Solution Approach 1:
The memory controller receives status data from the system level cache memory in advance, before the read operation is fully serviced. This preliminary receipt of status data allows the controller to make informed purge decisions without delaying the actual read operation service, as the status data is available early in the process timeline.
Solution Approach 2:
The memory controller continuously manages the pre-fetch buffer by making purge decisions based on available status data without interrupting the read operation service flow. The controller maintains continuous operation by using the status data to guide buffer management decisions in parallel with the read operation processing, rather than creating a sequential bottleneck.
Data Source
AI summary
Various embodiments include techniques for managing pre-fetch data in a computing system. A memory controller receives pre-fetch operations from a pre-fetch generator associated with a processing unit. The pre-fetch operations identify data that is likely to be accessed by the processing unit in the near future. In response, the memory controller retrieves read data associated with the read operations from system memory and stores the read data in a pre-fetch buffer included in the memory controller. The memory controller further receives status data via a low-latency signal path. The status data indicates information about each read operation, such as if the read operation can be serviced by a cache memory and whether the read operation is delayed but is to be transmitted to the memory controller. In response, the memory controller purges data from or holds data in the pre-fetch buffer based on the status data.