Messages in this thread | | | Date | Wed, 31 Jan 2018 11:17:10 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS |
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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.
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