On Wed, Jan 31, 2018 at 10:22:49AM +0100, Rafael J. Wysocki wrote: > On Tuesday, January 30, 2018 2:15:31 PM CET Peter Zijlstra wrote:
> > IA32_HWP_REQUEST has "Minimum_Performance", "Maximum_Performance" and > > "Desired_Performance" fields which can be used to give explicit > > frequency hints. And we really _should_ be doing that. > > > > Because, esp. in this scenario; a task migrating; the hardware really > > can't do anything sensible, whereas the OS _knows_. > > But IA32_HWP_REQUEST is not a cheap MSR to write to. That just means we might need to throttle writing to it, like it already does for the regular pstate (PERF_CTRL) msr in any case (also, is that a cheap msr?) Not touching it at all seems silly. But now that you made me look, intel_pstate_hwp_set() is horrible crap. You should _never_ do things like: rdmsr_on_cpu() /* frob value */ wrmsr_on_cpu() That's insane.
