linux-kernel - Re: Regression in 4.8 - CPU speed set very low

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Message-ID: <2937567e-57c7-b3f3-9668-3554de057e3d@lwfinger.net>
Date:   Fri, 30 Sep 2016 16:52:11 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Zhang Rui <rui.zhang@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: Regression in 4.8 - CPU speed set very low

On 09/29/2016 10:56 AM, Srinivas Pandruvada wrote:
> On Thu, 2016-09-29 at 14:19 +0200, Rafael J. Wysocki wrote:
>
> [...]
>
>>> My laptop was inadvertently put to sleep while I was gone. I forgot
>>> to leave a
>>> note for my wife and she quieted the noisy cpu fan. :)
>> It looks like in 4.8-rc we made a change that caused the "high" trip
>> point to
>> be acted on.
> This high trip point we don't expose in thermal subsystem (the thermal
>  zone dump didn't show this anywhere as a trip). This is exposed by
> core-dts driver only. This is the point BIOS is supposed to act, I
> guess that's why you are seeing 50% clock modulation.
>
>
> Are you running thermald
>
> What is?
> # ps -e | grep thermald
>
>
>>
>> Srinivas, Rui, do you recall what that can be?
>>
>> One more question (I think I asked it previously): In the failing
>> case
>> (4.8-rc1 and later), when the frequency drops down to the 400 MHz,
>> does it
>> ever go back higher or is it stuck at that level forever?
>>
>> In any case, it may help to file a bug at bugzilla.kernel.org against
>> CPU/thermal or similar and let me know the bug number.  We'll need to
>> collect some tracepoint data to debug this and some place to put them
>> into for easy reference.
> Yes, this is good idea.

To complete the record in this thread, the problem also happened with kernel 
4.7, thus it is not a regression in 4.8-rcX. The full discussion is at 
https://bugzilla.kernel.org/show_bug.cgi?id=173361.

Larry