Messages in this thread |  | | Subject | Re: [RFC/RFT][PATCH 4/7] cpuidle: menu: Split idle duration prediction from state selection | From | "Li, Aubrey" <> | Date | Tue, 6 Mar 2018 10:15:10 +0800 |
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On 2018/3/5 21:53, Peter Zijlstra wrote: > On Mon, Mar 05, 2018 at 02:05:10PM +0100, Rafael J. Wysocki wrote: >> On Mon, Mar 5, 2018 at 1:50 PM, Peter Zijlstra <peterz@infradead.org> wrote: >>> On Mon, Mar 05, 2018 at 12:47:23PM +0100, Rafael J. Wysocki wrote: > >>>> IOW, the target residency of the selected state doesn't tell you how >>>> much time you should expect to be idle in general. >>> >>> Right, but I think that measure isn't of primary relevance. What we want >>> to know is: 'should I stop the tick' and 'what C state do I go to'.
I understood the benefit of mapping duration to state number, is duration <-> state number mapping a generic solution to all arches?
Back to the user's concern is, "I'm running a latency sensitive application, and I want idle switching ASAP". So I think the user may not care about what C state to go into, that is, even if a deeper state has chance to go, the user striving for a higher workload score may still not want it?
>>> >>> In order to answer those questions we need durations as input, but I >>> don't think we should preserve durations throughout. The scheme from the >>> above link reduces to N states in order to deal with arbitrary >>> distributions, only the actual states -- ie boundaries where our answers >>> changes -- are relevant, anything inside those boundaries would lead to >>> the exact same answer anyway. >> >> I generally agree here, but I'm not convinced about flagging the >> states, splitting them and so on. > > I think linking them like that makes sense, but I can see room for > discussion... > >> Maybe just return a "nohz" indicator from cpuidle_select() in addition >> to the state index and make the decision in the governor? > > Much better option than returning a duration :-) > So what does "nohz = disable and state index = deepest" mean? This combination does not make sense for performance only purpose?
Thanks, -Aubrey
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