linux-kernel - Re: [RFT][PATCH v4 1/7] time: tick-sched: Reorganize idle tick management code

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Message-ID: <20180314172016.GO4064@hirez.programming.kicks-ass.net>
Date:   Wed, 14 Mar 2018 18:20:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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: [RFT][PATCH v4 1/7] time: tick-sched: Reorganize idle tick
 management code

On Wed, Mar 14, 2018 at 04:49:39PM +0100, Frederic Weisbecker wrote:
> On Mon, Mar 12, 2018 at 10:47:41AM +0100, Rafael J. Wysocki wrote:

> > @@ -136,6 +138,13 @@ static inline u64 get_cpu_idle_time_us(i
> >  static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
> >  #endif /* !CONFIG_NO_HZ_COMMON */
> >  
> > +static inline void tick_nohz_idle_stop_tick_protected(void)
> > +{
> > +	local_irq_disable();
> > +	tick_nohz_idle_stop_tick();
> > +	local_irq_enable();
> > +}
> 
> It seems that even if we have CONFIG_NO_HZ_COMMON=n,
> tick_nohz_idle_stop_tick_protected() will have overhead, right?

IIRC the only callsite of the _protected thing that remains at the end
is in the hotplug path. So who cares ;-)