linux-kernel - Re: Skylake (XPS 13 9350) TSC is way off

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Message-ID: <CALCETrVPrhXqqPP-7DMF6YHrBacm-tWBrSweF3_bZ7oPH5gsig@mail.gmail.com>
Date:	Wed, 2 Dec 2015 15:59:28 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"Brown, Len" <len.brown@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	"Hunter, Adrian" <adrian.hunter@...el.com>
Subject: Re: Skylake (XPS 13 9350) TSC is way off

On Wed, Dec 2, 2015 at 3:42 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Wed, Dec 2, 2015 at 3:38 PM, John Stultz <john.stultz@...aro.org> wrote:
>> On Wed, Dec 2, 2015 at 3:25 PM, Andy Lutomirski <luto@...nel.org> wrote:
>>> In case it's at all useful, adjtimex -p says:
>>>
>>>          mode: 0
>>>        offset: 0
>>>     frequency: 135641
>>>      maxerror: 37498
>>>      esterror: 1532
>>>        status: 8192
>>> time_constant: 2
>>>     precision: 1
>>>     tolerance: 32768000
>>>          tick: 10000
>>>      raw time:  1449098317s 671243180us = 1449098317.671243180
>>>
>>> this suggests a rather small correction, so I really have no idea what
>>> "Adjusting tsc more than 11% (8039115 vs 7759462)" means.
>>>
>>> John, you wrote this code.  What does the error message mean?
>
> Also, is there a behavior issue you're seeing or is this just a
> concern about the warning? I assumed it was the first, but digging up
> the thread here I'm not sure I see any specific problems listed.

No, there's no actual problem I'm aware of other than the error
message.  Skylake's TSC is different from other chips, and this is
Skylake, and I was worried that something was wrong with the initial
calibration.  It seems like the initial calibration may be fine,
though.

--Andy
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