Author Topic: Myths Programmers Believe about CPU Caches  (Read 942 times)

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Myths Programmers Believe about CPU Caches
« on: May 02, 2018, 09:42:58 AM »
As a computer engineer who has spent half a decade working with caches at Intel and Sun, I’ve learnt a thing or two about cache-coherency. This was one of the hardest concepts to learn back in college – but once you’ve truly understood it, it gives you a great appreciation for system design principles.

You might be wondering why you as a software developer should care about CPU cache-design. For one thing, many of the concepts learnt in cache-coherency are directly applicable to distributed-system-architecture and database-isolation-levels as well. For instance, understanding how coherency is implemented in hardware caches, can help in better understanding strong-vs-eventual consistency. It can spur ideas on how to better enforce consistency in distributed systems, using the same research and principles applied in hardware.

For another thing, misconceptions about caches often lead to false assertions, especially when it comes to concurrency and race conditions. For example, the common refrain that concurrent programming is hard because “different cores can have different/stale values in their individual caches”. Or that the reason we need volatiles in languages like Java, is to “prevent shared-data from being cached locally”, and force them to be “read/written all the way to main memory”.