Multiprocessor Cache Prefetch Bandwidth Allocation
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Solution Overview
Problem
In multiprocessor systems, the increasing number of processor cores leads to limited off-chip bandwidth due to pin constraints, resulting in latency and inefficient use of resources, as prefetches often go unused and waste limited off-chip bandwidth.
Innovation Solution
A prefetch bandwidth allocator assigns a higher proportion of off-chip bandwidth to processor cores with higher prefetch efficacy scores, based on the effectiveness and timeliness of their prefetched blocks, using a token system to manage and allocate bandwidth efficiently across cores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of processor cores is increased, then processing capabilities are improved, but off-chip bandwidth becomes limited due to pin constraints
Solution Approach 1:
The system dynamically changes the parameter of bandwidth allocation by adjusting prefetch bandwidth limits for different cores based on their prefetch efficacy scores. This allows the system to adapt bandwidth distribution to match actual prefetch performance, resolving the contradiction between increased core count and limited total bandwidth.
2Loss of time
If prefetching is used to reduce memory access latency, then execution time is reduced, but bandwidth is wasted when prefetched blocks are not used
Solution Approach 1:
The system implements feedback by monitoring prefetch efficacy scores for each core and using this information to dynamically adjust prefetch bandwidth allocation. Cores with higher efficacy scores receive more bandwidth, while those with lower scores receive less, ensuring bandwidth is allocated to prefetches that are actually useful and reducing waste from ineffective prefetching.
3Ease of operation
If prefetch bandwidth is allocated equally across all cores, then simplicity is maintained, but efficiency decreases when some cores have ineffective prefetches
Solution Approach 1:
The system applies local quality by allocating different prefetch bandwidth limits to different cores based on their individual prefetch efficacy scores. Instead of uniform allocation, each core receives a customized bandwidth limit that reflects its actual prefetch performance, optimizing overall system efficiency while maintaining manageable complexity through automated score-based differentiation.
Data Source
AI summary
Technologies are generally described for allocating available prefetch bandwidth among processor cores in a multiprocessor computing system. The prefetch bandwidth associated with an off-chip memory interface of the multiprocessor may be determined, partitioned, and allocated across multiple processor cores.