Cisco UCS C890 M5, Instruction Manual, Page: 107 / 191

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Stale AtoS (A to S)
The in-memory directory has three states: I, A, and S states. The I (-invalid) state indicates
that the data is clean and does not exist in the cache of any other sockets. The A (-snoop All)
state indicates that the data may exist in another socket in an exclusive or modified state.
The S state (-Shared) indicates that the data is clean and may be shared in the caches across
one or more sockets. When the system is performing "read" on the memory and if the
directory line is in A state, we must snoop all other sockets because another socket may
have the line in a modified state. If this is the case, a "snoop" will return the modified data.
However, it may be the case that a line "reads" in an A state, and all the snoops come back
with a "miss". This can happen if another socket reads the line earlier and then has silently
dropped it from its cache without modifying it. If the "Stale AtoS" feature is enabled, a line
will transition to the S state when the line in the A state returns only snoop misses. That
way, subsequent reads to the line will encounter it in the S state and will not have to snoop,
saving the latency and snoop bandwidth. Stale "AtoS" may be beneficial in a workload where
there are many cross-socket reads. The options are Disable, Enable, and Auto .
LLC Dead Line Alloc
Select Enable to opportunistically fill the deadlines in the LLC. The options are Enable ,
Disable, and Auto.
Isoc Mode
Select Enable to enable Isochronous support to meet QoS (Quality of Service) requirements.
This feature is especially important for Virtualization Technology. The options are Disable,
Enable, and Auto .
Memory Configuration
Enforce POR (Plan of Record)
Select POR to enforce POR restrictions for DDR4 memory frequency and voltage
programming. The options are POR and Disable.
PPR Type