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amolakn

Can someone clarify the meaning of BusRdX? Is this essentially just saying that some other processor is doing a cache read because it needs to read the current value before writing? Or is it saying that it's simply doing a memory read, but it's just likely that it'll write to it soon so we treat it as a write in the eyes of the other processors?

bpr

@amloakn, BusRdX indicates that the processor needs the data and it needs the permission to modify. The BusRdX is issued whenever the processor is executing a write, even if the processor is about to overwrite the entire cache line.

Generally, you never want to request more permissions than you need, since the permissions take away from other processors. That said, there is occasionally research on making BudRdX even if the processor is only just reading the data.