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From: Miroslav Lichvar <mlichvar@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>,
	Christopher Hall <christopher.s.hall@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-rt-users <linux-rt-users@vger.kernel.org>,
	jesus.sanchez-palencia@intel.com,
	Gavin Hindman <gavin.hindman@intel.com>,
	liam.r.girdwood@intel.com, Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: TSC to Mono-raw Drift
Date: Fri, 2 Nov 2018 12:20:06 +0100	[thread overview]
Message-ID: <20181102112006.GM19434@localhost> (raw)
In-Reply-To: <alpine.DEB.2.21.1811011859590.1642@nanos.tec.linutronix.de>

On Thu, Nov 01, 2018 at 07:03:37PM +0100, Thomas Gleixner wrote:
> On Thu, 1 Nov 2018, John Stultz wrote:
> > On Thu, Nov 1, 2018 at 10:44 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > > On Tue, 23 Oct 2018, John Stultz wrote:
> > >> However, to be correct, the ntp adjustments made would have to be made
> > >> to both the base interval + error, which mucks the math up a fair bit.
> > >
> > > Hmm, confused as usual. Why would you need to do anything like that?
> > 
> > Because the NTP adjustment is done off of what is now the raw clock.
> > If the raw clock is "corrected" the ppb adjustment has to be done off
> > of that corrected rate.
> 
> Sure, but why would that require any change? Right now the raw clock is
> slightly off and you correct clock monotonic against NTP. So with that
> extra correction you just see a slightly different raw clock slew and work
> from there.

It makes sense to me.

I think there are basically two different ways how it could be done.
One is to correct the frequency of the raw clock, on which sits the
mono/real clock. The other is to create a new raw clock which is
separate from the mono/real clock, and add an offset to the NTP
frequency to match the frequencies of the two clocks when not
synchronized by NTP/PTP. The latter would provide a more stable
mono/real clock.

clocksource -> MONOTONIC_RAW -> MONOTONIC/REALTIME

or 

clocksource -> ? -> MONOTONIC_RAW
                 -> MONOTONIC/REALTIME

-- 
Miroslav Lichvar

  reply	other threads:[~2018-11-02 11:20 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20181015160945.5993-1-christopher.s.hall@intel.com>
2018-10-19 15:25 ` Thomas Gleixner
2018-10-19 18:34   ` John Stultz
2018-10-19 18:39     ` John Stultz
2018-10-19 18:37   ` Thomas Gleixner
2018-10-19 18:48     ` John Stultz
2018-10-19 18:57       ` Thomas Gleixner
2018-10-19 19:21         ` John Stultz
2018-10-19 20:50           ` Thomas Gleixner
2018-10-19 22:36             ` John Stultz
2018-10-23 18:31               ` John Stultz
2018-10-24 14:51                 ` Miroslav Lichvar
2018-10-24 17:32                   ` Christopher Hall
2018-10-25 11:49                     ` Miroslav Lichvar
2018-11-01 17:41                   ` Thomas Gleixner
2018-11-02 10:26                     ` Miroslav Lichvar
2018-11-02 11:27                       ` Thomas Gleixner
2018-11-01 17:44                 ` Thomas Gleixner
2018-11-01 17:56                   ` John Stultz
2018-11-01 18:03                     ` Thomas Gleixner
2018-11-02 11:20                       ` Miroslav Lichvar [this message]
2018-11-02 11:25                         ` Thomas Gleixner
2018-11-02 12:31                           ` Miroslav Lichvar

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