linux-kernel - Re: [PATCH 2/2 (v2)] kselftest: timers: Add adjtick test to validate adjtimex() tick adjustments

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Message-ID: <CALAqxLXER0Bh2rrAN=rwNDu5AJLF3sqmkXa-KjJReZc8w6QtCw@mail.gmail.com>
Date:	Fri, 2 Oct 2015 13:27:15 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Miroslav Lichvar <mlichvar@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Nuno Gonçalves <nunojpg@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 2/2 (v2)] kselftest: timers: Add adjtick test to validate
 adjtimex() tick adjustments

On Fri, Oct 2, 2015 at 1:25 PM, John Stultz <john.stultz@...aro.org> wrote:
> On Mon, Sep 14, 2015 at 7:48 AM, Miroslav Lichvar <mlichvar@...hat.com> wrote:
>> Is there a cheap way to calculate this?
>> xtime_remainder * (ntp_tick >> ntp_error_shift) / NTP_INTERVAL_LENGTH
>
>
>
> Hrm.. So
>    xtime_remainder = (NTP_INTERVAL_LENGTH <<
> tk->tkr_mono.clock->shift) - (tk->cycle_interval *
> tk->tkr_mono.clock->mult)
>
>    for simplificiation:
>
> And we want to scale it as you pointed out above (though slightly
> fixed here) by:
>          (tk->ntp_tick >> tk->ntp_error_shift) / (NTP_INTERVAL_LENGTH
> << tk->tkr_mono.clock->shift)
>
>
> So this comes  out to:
>
>
> (tk->ntp_tick ) -  (tk->ntp_tick ) *  (tk->cycle_interval *
> tk->tkr_mono.clock->mult) / (NTP_INTERVAL_LENGTH <<
> tk->tkr_mono.clock->shift)
> tk->ntp_error_shift
>
>
>
> would:
>
> xtime_remainder = (tk->ntp_tick >> ntp_error_shift) - tk->xtime_interval
>
> After we've adjusted xtime_interval give us the equivalent?

Bah.. Ignore the above here. I was still working out a calculation and
accidentally hit send.

-john
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