Prefetch Cache Segmentation for CPU Data Starvation
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Solution Overview
Problem
High-speed CPUs experience significant idle time due to data starvation, with existing solutions like increasing cache size, memory speed, and bandwidth being costly and inefficient, and prior art solutions such as additional caches in the Northbridge architecture failing to effectively alleviate CPU data starvation.
Innovation Solution
A memory controller with a prefetch cache that includes a short-term and long-term storage portion, interfacing the CPU to system memory via a system memory bus, allowing for sequential prefetching of data when the bus is idle, reducing latency and CPU idle time without increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the size of the caches (L1 and L2) is increased to reduce CPU idle time, then CPU data availability improves, but the overall cost of the CPU increases significantly due to larger die size
Solution Approach 1:
The invention segments the cache system into three distinct parts: L1 cache within the CPU, L2 cache in the Northbridge, and a new prefetch cache also in the Northbridge. This segmentation allows each cache to serve specific purposes - L1 for immediate CPU needs, L2 for general storage, and the prefetch cache specifically for pre-loading data during idle periods, thereby reducing CPU idle time without requiring a single oversized cache that would increase die size
Solution Approach 2:
The prefetch cache acts as an intermediary between the L2 cache and the CPU. It pre-fetches data from L2 cache during idle periods and makes it available to the CPU before the CPU needs it, effectively mediating the data flow to reduce CPU waiting time without requiring the CPU itself to be larger or more complex
2Loss of time
If the system memory speed is increased to reduce CPU idle time, then data transfer speed improves, but the cost of the system increases due to expensive high-performance memory chips
Solution Approach 1:
The prefetch cache performs preliminary action by pre-fetching data from system memory into the Northbridge cache during idle periods. This advance data loading ensures that when the CPU needs data, it is already available in the faster Northbridge cache, eliminating the need to use slower but cheaper system memory at critical moments without requiring expensive high-speed memory chips
3Loss of time
If the bandwidth of the system memory bus is increased to reduce CPU idle time, then data transfer capacity improves, but the architecture of the overall computer system must be redesigned with new support chips
Solution Approach 1:
The prefetch cache enables self-service by utilizing idle periods on the existing system memory bus to pre-load data. Instead of requiring a higher-bandwidth bus that would demand architectural redesign, the system serves itself by productively using otherwise wasted idle time to prepare data for future CPU needs, maintaining compatibility with existing bus architecture
4Loss of time
If an additional cache is placed in the Northbridge to alleviate CPU data starvation, then data availability to CPU improves, but the cache size is typically much smaller than L1 and L2 caches, limiting effectiveness
Solution Approach 1:
The prefetch cache in the Northbridge performs preliminary data loading during idle periods, accumulating data in advance. This preliminary action allows the cache to maintain a smaller size while still being effective, because it fills up strategically during idle time rather than needing to maintain large capacity continuously like traditional caches
Data Source
AI summary
A memory controller for prefetching data for a processor, or CPU, of a computer system. The memory controller functions by interfacing the processor to system memory via a system memory bus. A prefetch cache is included in the memory controller. The prefetch cache includes a short-term storage portion and a long-term storage portion. The prefetch cache is configured to access system memory to retrieve and store a plurality of sequential cache lines subsequent to a processor access to system memory.