>> >> It makes sense having to know what the dependencies are before we >> change processor speeds. But what about just asking what the current >> speed is (not changing it) so that it can be initialized...or is there >> no way to ask, and we have to change it to know? >Unfortunately, I don't think that's doable. It's one of the few things >that I don't like about the way Intel implemented P-states. Reading the >status MSR will not allow you to determine your current P-state. I >believe you have to set it to be certain. I think that the same is true >of SPARC. >
The spec Vol3.a 13.1.1 states IA32_PERF_STATUS is updated dynamically. And you can query IA32_PERF_CTL to determine what was last requested. Its just discouraged to make determination based on these since these are Model specific. Ideally we should use APERF/MPERF since is architecturally defined (as indicated by cpuid.6 to get the feedback mechanism to make P state decisions? Cheers, ashok
