On: Common Systems Programming Optimizations and Trick...

[y7]

> Now, to support multiple processors on a single machine reading and writing from the same memory in a coherent way, only one processor on a machine can have exclusive access to a given cache line.

Does this also apply when multiple processors are only reading memory?

[atq2119 → y7]

No. That's what MESI-based cache protocols are all about. Multiple cores/processors can have the same cache line in a shared/read-only state. Only writes require exclusive access.

[ncmncm → y7]

"Exclusive access" means writing. But the reader doesn't know when it might change. Sometimes that's exactly what you want.