linux-kernel - Re: TSC to Mono-raw Drift

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Message-ID: <alpine.DEB.2.21.1811011841060.1642@nanos.tec.linutronix.de>
Date:   Thu, 1 Nov 2018 18:44:57 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     John Stultz <john.stultz@...aro.org>
cc:     Christopher Hall <christopher.s.hall@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        jesus.sanchez-palencia@...el.com,
        Gavin Hindman <gavin.hindman@...el.com>,
        liam.r.girdwood@...el.com, Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Miroslav Lichvar <mlichvar@...hat.com>
Subject: Re: TSC to Mono-raw Drift

On Tue, 23 Oct 2018, John Stultz wrote:
> On Fri, Oct 19, 2018 at 3:36 PM, John Stultz <john.stultz@...aro.org> wrote:
> I spent a little bit of time thinking this out. Unfortunately I don't
> think its a simple matter of calculating the granularity error on the
> raw clock and adding it in each interval. The other trouble spot is
> that the adjusted clocks (monotonic/realtime) are adjusted off of that
> raw clock. So they would need to have that error added as well,
> otherwise the raw and a otherwise non-adjusted monotonic clock would
> drift.
> 
> 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?

Thanks,

	tglx