It is not cheap enough, yet. Rationale: although it could be easy to account user processes, it would not be that easy for the OS kernel and kernel components (

It is not cheap enough, yet. Rationale: although it could be easy to account user processes, it would not be that easy for the OS kernel and kernel components (e.g. figure how to account cache pollution because of hardware IRQ dispatching and devices doing DMA...). So, except for, may be, micro-kernel OS's, and adding performance counters to every single device capable of bus-mastering, it is far from being a reality, in my opinion.