顺序一致性是否蕴含缓存一致性？

Hey folks, let's unpack how sequential consistency relates to cache consistency, and why the former implies the latter:

Cache Consistency Basics #

Cache consistency is all about ensuring shared memory behaves predictably across multiple processors, with three core guarantees:

• Any read operation must return the most recently written value for that memory location.
• Every write you perform will eventually be visible to subsequent reads (no writes vanish into the ether).
• All processors will observe writes to the same memory location in the exact same order.

Sequential Consistency: A Stricter Model #

Sequential consistency raises the bar with even tighter rules for memory operations:

• There’s a single global total order that applies to all memory operations (reads and writes) across every processor in the system.
• Each operation is atomic—from the perspective of other processors, it looks like it completed instantly.
• This global order has to respect the program order of each individual processor: if your code does operation A then operation B on one CPU, the global order will never have B come before A.

Why Sequential Consistency Covers Cache Consistency #

If a system follows sequential consistency, it automatically checks all the boxes for cache consistency:

1. Latest write on reads: Since there’s a global order, any read will always see the last write that precedes it in this order—so it’s guaranteed to be the most recent value.
2. Writes are eventually visible: Every write is part of that global sequence, so eventually any read that comes after it in the order will pick it up.
3. Uniform write order: The global total order ensures every processor sees writes to a location in the same sequence, which directly satisfies the third cache consistency rule.

In short: sequential consistency is a stricter memory model than cache consistency. Any system that’s sequentially consistent is automatically cache-consistent, but a cache-consistent system might not meet the more rigid global order and program order requirements of sequential consistency.

内容的提问来源于stack exchange，提问作者Owe u.