linux-kernel - Re: [RFC/RFT][PATCH v2 1/6] time: tick-sched: Reorganize idle tick management code

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Message-ID: <20180307231827.GA9367@lerouge>
Date:   Thu, 8 Mar 2018 00:18:29 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Rik van Riel <riel@...riel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/RFT][PATCH v2 1/6] time: tick-sched: Reorganize idle tick
 management code

On Tue, Mar 06, 2018 at 10:02:01AM +0100, Rafael J. Wysocki wrote:
> Index: linux-pm/kernel/time/tick-sched.c
> ===================================================================
> --- linux-pm.orig/kernel/time/tick-sched.c
> +++ linux-pm/kernel/time/tick-sched.c
> +
> +/**
> + * tick_nohz_idle_prepare - prepare for entering idle on the current CPU.
> + *
> + * Called when we start the idle loop.
> + */
> +void tick_nohz_idle_prepare(void)
> +{
> +	struct tick_sched *ts;
> +
> +	__tick_nohz_idle_prepare();
> +
> +	local_irq_disable();
> +
> +	ts = this_cpu_ptr(&tick_cpu_sched);
> +	ts->inidle = 1;
> +
> +	local_irq_enable();
> +}

Why not calling tick_nohz_start_idle() from there? This is going to
simplify the rest, you won't need to call tick_nohz_idle_go_idle()
from places that don't want to stop the tick and you can then remove
the stop_tick argument.

> +
> +/**
> + * tick_nohz_idle_go_idle - start idle period on the current CPU.
> + * @stop_tick: Whether or not to stop the idle tick.
> + *
> + * When @stop_tick is set and the next event is more than a tick into the
> + * future, stop the idle tick.
> + */
> +void tick_nohz_idle_go_idle(bool stop_tick)
> +{
> +	__tick_nohz_idle_enter(this_cpu_ptr(&tick_cpu_sched), stop_tick);
> +}
> +
> +void tick_nohz_idle_enter(void)
> +{
> +	struct tick_sched *ts;
> +
> +	__tick_nohz_idle_prepare();
>  
>  	local_irq_disable();
>  
>  	ts = this_cpu_ptr(&tick_cpu_sched);
>  	ts->inidle = 1;
> -	__tick_nohz_idle_enter(ts);
> +	__tick_nohz_idle_enter(ts, true);
>  
>  	local_irq_enable();
>  }

Ah I see you're keeping tick_nohz_idle_enter() around because of the callsite
in xen. It looks like a hack (from the xen part), I'll need to have a look at
it, just a note for myself...

Thanks.