lkml.org 
[lkml]   [2018]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRE: [RFT][PATCH v7 5/8] cpuidle: Return nohz hint from cpuidle_select()
    Date
    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.
    >
    > 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).

    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).

    http://fast.smythies.com/rjw_v72p_idle.png

    ... Doug


    \
     
     \ /
      Last update: 2018-03-22 07:25    [W:2.209 / U:0.352 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site