2.1.2 Fully-coherent Home Node

The Fully-coherent Home Node (HN-F) is responsible for managing part of the address space.

The HN-F consists of the following:

L3 cacheThe L3 cache is a distributed, mostly exclusive last-level cache. The L3 cache-allocation policy is exclusive for data lines, except where sharing patterns are detected, and pseudo-inclusive for code lines, as controlled by the RN-Fs, meaning that all code lines can be allocated into the L3 on the initial request.
Combined PoS/PoCThe combined Point-of-Serialization/Point-of-Coherency (PoS/PoC) is responsible for the ordering of all memory requests sent to the HN-F. This includes coherency ordering, that is, serialization of multiple outstanding requests and actions to the same line, and request ordering as required by the RNs.
Snoop filterThe snoop filter reduces snoop coherency traffic in the system by tracking cache lines that are present in the RN-Fs in the system, and generally converting snoop broadcasts to directed snoops. This substantially reduces the quadratic growth in snoop response traffic that might otherwise be required without the snoop filter.

Each HN-F in the system is configured to manage a specific portion of the overall address space, and all three functionalities are included in this management responsibility:

Therefore, the entire memory address space is managed through the combination of all HN-Fs in the system, except for the memory-mapped I/O address space.

Note:

The HN-F is architecturally defined to manage only well-behaved memory, that is, memory without any possible side effects. The HN-F includes microarchitectural optimizations to exploit this architectural guarantee.
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