Re: [PATCH v9 05/10] cpuidle: Return nohz hint from cpuidle_select()

[Frederic Weisbecker]

On Fri, Apr 06, 2018 at 10:11:04AM +0200, Rafael J. Wysocki wrote:
> On Friday, April 6, 2018 4:44:14 AM CEST Frederic Weisbecker wrote:
> > On Wed, Apr 04, 2018 at 10:39:50AM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > > Index: linux-pm/kernel/time/tick-sched.c
> > > ===================================================================
> > > --- linux-pm.orig/kernel/time/tick-sched.c
> > > +++ linux-pm/kernel/time/tick-sched.c
> > > @@ -991,6 +991,20 @@ void tick_nohz_irq_exit(void)
> > >  }
> > >  
> > >  /**
> > > + * tick_nohz_idle_got_tick - Check whether or not the tick handler has run
> > > + */
> > > +bool tick_nohz_idle_got_tick(void)
> > > +{
> > > +	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
> > > +
> > > +	if (ts->inidle > 1) {
> > > +		ts->inidle = 1;
> > > +		return true;
> > > +	}
> > > +	return false;
> > > +}
> > > +
> > > +/**
> > >   * tick_nohz_get_sleep_length - return the length of the current sleep
> > >   *
> > >   * Called from power state control code with interrupts disabled
> > > @@ -1101,6 +1115,9 @@ static void tick_nohz_handler(struct clo
> > >  	struct pt_regs *regs = get_irq_regs();
> > >  	ktime_t now = ktime_get();
> > >  
> > > +	if (ts->inidle)
> > > +		ts->inidle = 2;
> > > +
> > 
> > You can move that to tick_sched_do_timer() to avoid code duplication.
> > 
> > Also these constants are very opaque. And even with proper symbols it wouldn't look
> > right to extend ts->inidle that way.
> > 
> > Perhaps you should add a field such as ts->got_idle_tick under the boolean fields
> > after the below patch:
> > 
> > --
> > From c7b2ca5a4c512517ddfeb9f922d5999f82542ced Mon Sep 17 00:00:00 2001
> > From: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > Date: Fri, 6 Apr 2018 04:32:37 +0200
> > Subject: [PATCH] nohz: Gather tick_sched booleans under a common flag field
> > 
> > This optimize the space and leave plenty of room for further flags.
> > 
> > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > ---
> >  kernel/time/tick-sched.h | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
> > index 954b43d..38f24dc 100644
> > --- a/kernel/time/tick-sched.h
> > +++ b/kernel/time/tick-sched.h
> > @@ -45,14 +45,17 @@ struct tick_sched {
> >  	struct hrtimer			sched_timer;
> >  	unsigned long			check_clocks;
> >  	enum tick_nohz_mode		nohz_mode;
> > +
> > +	unsigned int			inidle		: 1;
> > +	unsigned int			tick_stopped	: 1;
> 
> This particular change breaks build, because tick_stopped is
> accessed via __this_cpu_read() in tick_nohz_tick_stopped().

Oops...

> 
> > +	unsigned int			idle_active	: 1;
> > +	unsigned int			do_timer_last	: 1;
> > +
> >  	ktime_t				last_tick;
> >  	ktime_t				next_tick;
> > -	int				inidle;
> > -	int				tick_stopped;
> >  	unsigned long			idle_jiffies;
> >  	unsigned long			idle_calls;
> >  	unsigned long			idle_sleeps;
> > -	int				idle_active;
> >  	ktime_t				idle_entrytime;
> >  	ktime_t				idle_waketime;
> >  	ktime_t				idle_exittime;
> > @@ -62,7 +65,6 @@ struct tick_sched {
> >  	unsigned long			last_jiffies;
> >  	u64				next_timer;
> >  	ktime_t				idle_expires;
> > -	int				do_timer_last;
> >  	atomic_t			tick_dep_mask;
> >  };
> >  
> > 
> 
> So what about this?  And moving the duplicated piece of got_idle_tick
> manipulation on top of it?
> 
> ---
> From: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Subject: [PATCH] nohz: Gather tick_sched booleans under a common flag field
> 
> Optimize the space and leave plenty of room for further flags.
> 
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> [ rjw: Do not use __this_cpu_read() to access tick_stopped and add
>        got_idle_tick to avoid overloading inidle ]
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Yeah looks good, thanks!