Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS | Date | Thu, 01 Feb 2018 08:50:28 +0100 |
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On Wednesday, January 31, 2018 11:17:10 AM CET Peter Zijlstra wrote: > 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.
OK
So what field precisely would you touch? "desired"? If so, does that actually guarantee anything to happen?
> 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.
I guess you mean it does too many IPIs? Or that it shouldn't do any IPIs at all?
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