linux-kernel - Re: [PATCH] x86/xen/time: set ->min_delta_ticks and ->max_delta

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Message-ID: <4a873fe9-ca70-b3bc-c101-f55ebc636a1b@suse.com>
Date:   Thu, 6 Apr 2017 11:11:31 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Nicolai Stange <nicstange@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] x86/xen/time: set ->min_delta_ticks and ->max_delta_ticks

On 30/03/17 22:06, Nicolai Stange wrote:
> 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 xen 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.
> 
> Signed-off-by: Nicolai Stange <nicstange@...il.com>

Shall I carry this patch through the Xen tree or will it be processed
via the tip tree? I'm fine with both variants.


Juergen

> ---
> 
> 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/xen/time.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 1e69956d7852..7a3089285c59 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -209,7 +209,9 @@ static const struct clock_event_device xen_timerop_clockevent = {
>  	.features		= CLOCK_EVT_FEAT_ONESHOT,
>  
>  	.max_delta_ns		= 0xffffffff,
> +	.max_delta_ticks	= 0xffffffff,
>  	.min_delta_ns		= TIMER_SLOP,
> +	.min_delta_ticks	= TIMER_SLOP,
>  
>  	.mult			= 1,
>  	.shift			= 0,
> @@ -268,7 +270,9 @@ static const struct clock_event_device xen_vcpuop_clockevent = {
>  	.features = CLOCK_EVT_FEAT_ONESHOT,
>  
>  	.max_delta_ns = 0xffffffff,
> +	.max_delta_ticks = 0xffffffff,
>  	.min_delta_ns = TIMER_SLOP,
> +	.min_delta_ticks = TIMER_SLOP,
>  
>  	.mult = 1,
>  	.shift = 0,
>