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 | Fri, 02 Feb 2018 12:00:08 +0100 |
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On Thursday, February 1, 2018 2:18:12 PM CET Srinivas Pandruvada wrote: > On Thu, 2018-02-01 at 10:11 +0100, Peter Zijlstra wrote: > > On Thu, Feb 01, 2018 at 08:50:28AM +0100, Rafael J. Wysocki wrote: > > > > > > 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? > > No idea, desired would be the one I would start with, it matches with > > the intent here. But I've no idea what our current HWP implementation > > actually does with it. > Desired !=0 will disable HWP autonomous mode of frequency selection.
But I don't think it will just run at "desired" then, will it?
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