linux-kernel - Re: [PATCH] x86/lguest/timer: set ->min_delta_ticks and ->max_delta

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Date:   Sun, 02 Apr 2017 11:05:14 +0930
From:   Rusty Russell <rusty@...tcorp.com.au>
To:     Nicolai Stange <nicstange@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paul Bolle <pebolle@...cali.nl>,
        Andy Lutomirski <luto@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, lguest@...ts.ozlabs.org
Subject: Re: [PATCH] x86/lguest/timer: set ->min_delta_ticks and ->max_delta_ticks

Nicolai Stange <nicstange@...il.com> writes:
> In preparation for making the clockevents core NTP correction aware,
> all clockevent device drivers must set ->min_delta_ticks and
> ->max_delta_ticks rather than ->min_delta_ns and ->max_delta_ns: a
> clockevent device's rate is going to change dynamically and thus, the
> ratio of ns to ticks ceases to stay invariant.
>
> Make the x86 arch's lguest clockevent driver initialize these fields
> properly.
>
> This patch alone doesn't introduce any change in functionality as the
> clockevents core still looks exclusively at the (untouched) ->min_delta_ns
> and ->max_delta_ns. As soon as this has changed, a followup patch will
> purge the initialization of ->min_delta_ns and ->max_delta_ns from this
> driver.

Acked-by: Rusty Russell <rusty@...tcorp.com.au>

>
> Signed-off-by: Nicolai Stange <nicstange@...il.com>
> ---
>
> Notes:
>     This prerequisite patch is part of a larger effort to feed NTP
>     corrections into the clockevent devices' frequencies and thus
>     avoiding their notion of time to diverge from the system's
>     one. If you're interested, the current state of the whole series
>     can be found at [1].
>     
>     If you haven't got any objections and these prerequisites get
>     merged by 4.12 everywhere, I'll proceed with the remainder of
>     this series in 4.13.
>     
>     Applicable to next-20170324 as well as to John' Stultz tree [2].
>     
>     [1]
>       git://nicst.de/linux.git cev-freq-adj.v10.fortglx-4.12-time
>       https://nicst.de/git/?p=linux.git;a=shortlog;h=refs/heads/cev-freq-adj.v10.fortglx-4.12-time
>     
>     [2]
>       https://git.linaro.org/people/john.stultz/linux.git fortglx/4.12/time
>
>  arch/x86/lguest/boot.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
> index d3289d7e78fa..3e4bf887a246 100644
> --- a/arch/x86/lguest/boot.c
> +++ b/arch/x86/lguest/boot.c
> @@ -994,7 +994,9 @@ static struct clock_event_device lguest_clockevent = {
>  	.mult                   = 1,
>  	.shift                  = 0,
>  	.min_delta_ns           = LG_CLOCK_MIN_DELTA,
> +	.min_delta_ticks        = LG_CLOCK_MIN_DELTA,
>  	.max_delta_ns           = LG_CLOCK_MAX_DELTA,
> +	.max_delta_ticks        = LG_CLOCK_MAX_DELTA,
>  };
>  
>  /*
> -- 
> 2.12.0