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Subject: Re: [RFT][PATCH v7 5/8] cpuidle: Return nohz hint from
 cpuidle_select()
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Doug Smythies <dsmythies@telus.net>,
        "Rik van Riel" <riel@surriel.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        "Mike Galbraith" <mgalbraith@suse.de>,
        LKML <linux-kernel@vger.kernel.org>
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From:   Thomas Ilsche <thomas.ilsche@tu-dresden.de>
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Date:   Wed, 21 Mar 2018 18:59:57 +0100
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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.