linux-kernel - Re: [PATCHv2] timekeeping: Update multiplier when NTP frequency is set directly

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Message-ID: <CALAqxLUh+A1nJF1n2G_pRPrUQPMD6b-9fAdojPmAOkmnUM+-Nw@mail.gmail.com>
Date:   Fri, 22 Jun 2018 14:12:28 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Miroslav Lichvar <mlichvar@...hat.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Richard Cochran <richardcochran@...il.com>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCHv2] timekeeping: Update multiplier when NTP frequency is
 set directly

On Fri, Jun 22, 2018 at 2:09 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Mon, 4 Jun 2018, Miroslav Lichvar wrote:
>
>> When the NTP frequency is set directly from userspace using the
>> ADJ_FREQUENCY or ADJ_TICK timex mode, immediately update the
>> timekeeper's multiplier instead of waiting for the next tick.
>>
>> This removes a hidden non-deterministic delay in setting of the
>> frequency and allows an extremely tight control of the system clock
>> with update rates close to or even exceeding the kernel HZ.
>>
>> The update is limited to archs using modern timekeeping
>> (!ARCH_USES_GETTIMEOFFSET).
>
> John ?????

Yea. I've got this in my toqueue list.  I'm going to take another pass
at testing and hopefully send it your way.

thanks
-john