linux-kernel - Re: [RFC PATCH v2 5/8] timers: keep sleep length updated as needed

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Message-ID: <1554921.dz8jk4n8cL@aspire.rjw.lan>
Date:   Sat, 14 Oct 2017 02:56:27 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Aubrey Li <aubrey.li@...el.com>
Cc:     tglx@...utronix.de, peterz@...radead.org, len.brown@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 5/8] timers: keep sleep length updated as needed

On Saturday, September 30, 2017 9:20:31 AM CEST Aubrey Li wrote:
> sleep length indicates how long we'll be idle. Currently, it's updated
> only when tick nohz enters. These patch series make a new requirement
> with tick, so we should keep sleep length updated as needed

So what exactly would be the problem with leaving things as they are?

> ---
>  kernel/time/tick-sched.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index d663fab..94fb9b8 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -1008,8 +1008,11 @@ void tick_nohz_irq_exit(void)
>   */
>  ktime_t tick_nohz_get_sleep_length(void)
>  {
> +	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
>  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
>  
> +	ts->sleep_length = ktime_sub(dev->next_event, ktime_get());
> +
>  	return ts->sleep_length;
>  }
>  
> 

I probably wouldn't do it this way ...