linux-kernel - Re: [PATCH] rtc: adapt allowed RTC update error

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Message-ID: <20201202153656.GC2231584@localhost>
Date:   Wed, 2 Dec 2020 16:36:56 +0100
From:   Miroslav Lichvar <mlichvar@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
        John Stultz <john.stultz@...aro.org>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH] rtc: adapt allowed RTC update error

On Wed, Dec 02, 2020 at 04:07:28PM +0100, Miroslav Lichvar wrote:
> On Wed, Dec 02, 2020 at 02:44:53PM +0100, Thomas Gleixner wrote:
> > Something like the completely untested below should make this reliable
> > and only needs to retry when the work is running late (busy machine),
> > but the wakeup will be on time or at max 1 jiffie off when high
> > resolution timers are not available or disabled.
> 
> It seems to work nicely. In my test most of the updates succeeded on
> the first attempt hitting the right tick, the rest succeeding on the
> second attempt. Only when the clock was set to run 10% faster, it
> needed few more attempts to converge to the target time.

I noticed an observable change wrt adjtimex() calls though. It seems
it now reschedules the RTC update, i.e. there can be more than one
update per 11 minutes. Was this intended?

> @@ -629,7 +618,7 @@ void ntp_notify_cmos_timer(void)
>  
>         if (IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE) ||
>             IS_ENABLED(CONFIG_RTC_SYSTOHC))
> -               queue_delayed_work(system_power_efficient_wq, &sync_work, 0);
> +               queue_work(system_power_efficient_wq, &sync_work);
>  }

-- 
Miroslav Lichvar