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    SubjectRe: [RFT][PATCH v7 5/8] cpuidle: Return nohz hint from cpuidle_select()
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    On Thursday, March 22, 2018 4:41:54 PM CET Doug Smythies wrote:
    > On 2018.03.21 23:25 Doug Smythies wrote:
    > > On 2018.03.21 15:15 Rafael J. Wysocki wrote:
    > >> On Wed, Mar 21, 2018 at 6:59 PM, Thomas Ilsche wrote:
    > >>> On 2018-03-21 15:36, Rafael J. Wysocki wrote:
    > >>>>
    > >>>> So please disregard this one entirely and take the v7.2 replacement
    > >>>> instead of it:https://patchwork.kernel.org/patch/10299429/
    > >>>>
    > >>>> The current versions (including the above) is in the git branch at
    > >>>>
    > >>>> git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git \
    > >>>> idle-loop-v7.2
    > >>>
    > >>> With v7.2 (tested on SKL-SP from git) I see similar behavior in idle
    > >>> as with v5: several cores which just keep the sched tick enabled.
    > >>> Worse yet, some go only in C1 (not even C1E!?) despite sleeping the
    > >>> full sched tick.
    > >>> The resulting power consumption is ~105 W instead of ~ 70 W.
    > >>>
    > >>> https://wwwpub.zih.tu-dresden.de/~tilsche/powernightmares/v7_2_skl_sp_idle.png
    > >>>
    > >>> I have briefly ran v7 and I believe it was also affected.
    >
    > I am not seeing any issues at all with V7.
    >
    > >>
    > >> Then it looks like menu_select() stubbornly thinks that the idle
    > >> duration will be within the tick boundary on those cores.
    > >>
    > >> That may be because the bumping up of the correction factor in
    > >> menu_reflect() is too conservative or it may be necessary to do
    > >> something radical to measured_us in menu_update() in case of a tick
    > >> wakeup combined with a large next_timer_us value.
    > >>
    > >> For starters, please see if the attached patch (on top of the
    > >> idle-loop-v7.2 git branch) changes this behavior in any way.
    > >
    > > O.K. I am seeing some weirdness.
    > > On my system with both V7.2 and V7.2 plus this patch, I observe
    > > A spike in Idle State 1 residency every 34+ minutes. And slightly
    > > higher average idle power than before.
    > > (I might not have done V7 idle tests long enough).
    >
    > I re-did the idle test on V7, and for longer.
    > It is great.
    > See line added to the idle graph for V7.2+:
    >
    > http://fast.smythies.com/rjw_v72p_v7_idle.png
    >
    > >
    > > It can be seen in the frequency sweep I did earlier today, with V7.2:
    > >
    > > http://fast.smythies.com/rjw_freq_sweep_72_combined.png
    > >
    > > Despite the note on the graph that says it might be real, I don't think
    > > it is (I forgot to delete the note).
    > >
    > > With V7.2+ sometimes the event occurs at 17 minute intervals.
    > > Here is a idle graph (for reference: we have seen idle package power
    > > pretty steady at ~3.7 watts before).
    >
    > Now shown on the new graph. Link above.

    Thanks for the data!

    I will send another update of patch [5/8] shortly which is closer to the
    original v7 of it than the v7.[1-2].

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