Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFT][PATCH v7 5/8] cpuidle: Return nohz hint from cpuidle_select() | Date | Thu, 22 Mar 2018 18:23:38 +0100 |
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On Thursday, March 22, 2018 2:18:59 PM CET Thomas Ilsche wrote: > On 2018-03-21 23:15, Rafael J. Wysocki wrote: > > On Wed, Mar 21, 2018 at 6:59 PM, Thomas Ilsche > > <thomas.ilsche@tu-dresden.de> 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. > > > > The patch on top of idle-loop-v7.2 doesn't improve idle behavior on > SKL-SP. Overall it is pretty erratic, I have not seen any regular > patterns. Sometimes only few cpus are affected, here's a screenshot of > almost all cpus being affected after a short burst workload. > > https://wwwpub.zih.tu-dresden.de/~tilsche/powernightmares/v7_2_reflect_skl_sp_idle.png
Thanks for the information!
I will post a v7.3 of patch [5/8] shortly that appears to give good results for me. It may be selectig deep states quite aggressively, but let's see.
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