On 04/15/2015 01:42 PM, Andy Lutomirski wrote: > > I disagree. We should try to NACK any new code that can't function > without MTRRs. > > (Plus, ARM is growing in popularity in the server space, and ARM quite > sensibly doesn't have MTRRs.) > <NOT SPEAKING FOR INTEL HERE> Yes. People need to understand that MTRRs are fundamentally a transitional solution, a replacement for the KEN# logic in the P4 and P5 generation processors. The KEN# logic in the chipset would notify the CPU that a specific address should not be cached, without affecting the software (which may have been written for x86s built before caching existed, even.) MTRRs move this to the head end, so the CPU knows ahead of time what to do, as is required with newer architectures. It also enabled write combining in a transparent fashion. However, it is still transitional; it is there to describe the underlying constraints of the memory system so that code which doesn't use paging can run at all, but the only thing that can actually scale is PAT. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
