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

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Message-ID: <CALAqxLXjH09M87nO5HOBLzLZ5qnb_-oQ0D17PpQWW4Z6L57ohg@mail.gmail.com>
Date:	Mon, 21 Dec 2015 13:56:24 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Jon Masters <jonathan@...masters.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 Mon, Dec 21, 2015 at 12:10 AM, Jon Masters <jonathan@...masters.org> wrote:
> On 12/2/15, 6:55 PM, John Stultz wrote:
>>
>> On Wed, Dec 2, 2015 at 3:42 PM, Andy Lutomirski <luto@...nel.org> wrote:
>
>
>>>> On a hunch, are you running chrony instead of ntpd?
>>>
>>>
>>> Yes, this is indeed chrony.
>>
>>
>> Ok. I'll have to look closer. The last time that message came up it
>> was in a report of a bug that chrony uncovered with the internal
>> correction being too slow. I know chrony is much more aggressive
>> compared to ntpd in tweaking the freq value for the initial converging
>> correction at startup, so maybe that along with something else is
>> causing us to get out of spec.
>
>
> Can you copy me on followup? I'm seeing similar behavior with chrony on
> recent kernels on a couple of different ARM server prototype systems.

A patch for this just landed in tip/timers/core and is pending for 4.5
http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=ec02b076ceab63f99e5b3d80fd223d777266c236

thanks
-john
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