Cache Probe Requests for I/O Data Stream Allocation
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Solution Overview
Problem
Modern computer processors face inefficiencies due to cache coherency issues when performing operations involving data that has been subject to direct memory access (DMA) operations, leading to potential misalignment of data copies in memory and caches, which can hinder performance.
Innovation Solution
A method and system where an allocator sends write probes to multiple caches to determine if the memory address for a data stream is present in any cache, allowing data to be directly written to the cache if found, thereby avoiding cache coherency issues and optimizing data allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data is copied to cache when not present, then processor performance is improved, but cache coherency issues arise when DMA operations modify memory data
Solution Approach 1:
The allocator performs preliminary actions by sending probe requests to caches before DMA operations to determine if data is already present in caches. This preliminary checking prevents subsequent cache coherency issues by identifying which caches hold copies of data that may be modified by DMA operations, allowing the system to invalidate or update those caches accordingly.
Solution Approach 2:
The system implements feedback mechanisms where cache responses to probe requests are used to determine subsequent actions. When a probe request returns a hit, the allocator receives feedback indicating data presence in cache, which triggers cache invalidation or update operations to maintain coherency. This feedback loop ensures cache consistency while preserving performance benefits.
2Reliability
If processor accesses memory to copy data to cache, then data availability for processing is improved, but access time increases due to memory operations
Solution Approach 1:
The allocator performs preliminary probing of caches before DMA operations to identify which caches already contain the required data. This preliminary action eliminates the need for subsequent memory access and data copying operations, directly reducing access time while ensuring data availability for processing.
Solution Approach 2:
Instead of universally copying all DMA-modified data from memory to caches, the system performs partial actions by only updating or invalidating specific cache lines that were identified as containing the modified data through probe requests. This selective approach reduces unnecessary memory access time while maintaining data availability where needed.
Data Source
AI summary
A method and system for allocating data streams that includes receiving, at an allocator, a data stream. The data stream includes a memory address and data associated with the memory address. The method also includes examining, by the allocator, the data stream to make a determination that the data stream is a soft allocating data stream, and then sending, from the allocator based on the determination, a plurality of write probes to a plurality of caches, wherein each write probe of the plurality of write probes includes at least part of the memory address. Additionally, the method includes receiving, at the allocator in response to a write probe of the plurality of write probes, a cache line present acknowledgement from a cache of the plurality of caches, and directing, by the allocator in response to the cache line present acknowledgement, the data of the data stream to the cache.