linux-kernel - Re: [PATCH 2/2] sched: Extract the task putting code from pick_next

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Date:   Tue, 21 Apr 2020 16:28:32 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 2/2] sched: Extract the task putting code from
 pick_next_task()

On Mon, Apr 20, 2020 at 06:32:32PM -0400, Steven Rostedt wrote:
> On Mon, 20 Apr 2020 00:31:52 +0800
> Chen Yu <yu.c.chen@...el.com> wrote:
> 
> > Introduce a new function finish_prev_task() to do the balance
> > when necessary, and then put previous task back to the run queue.
> > This function is extracted from pick_next_task() to prepare for
> > future usage by other type of task picking logic.
> > 
> > No functional change.
> > 
> > Suggested-by: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> > ---
> >  kernel/sched/core.c | 39 +++++++++++++++++++++++----------------
> >  1 file changed, 23 insertions(+), 16 deletions(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 3a61a3b8eaa9..bf59a5cf030c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -3904,6 +3904,28 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
> >  	schedstat_inc(this_rq()->sched_count);
> >  }
> >  
> > +static void finish_prev_task(struct rq *rq, struct task_struct *prev,
> > +			     struct rq_flags *rf)
> > +{
> > +	const struct sched_class *class;
> > +#ifdef CONFIG_SMP
> > +	/*
> > +	 * We must do the balancing pass before put_next_task(), such
> 
> I know this is just a cut and paste move, but I'm thinking that this
> comment is wrong. Shouldn't this be "put_prev_task()" as we have no
> "put_next_task()" function.
> 
>
Okay, I'll fix it in v3.
> > +	finish_prev_task(rq, prev, rf);
> 
> I'm not sure I like the name of this function. Perhaps
> "balance_and_put_prev_task()"? Something more in kind to what the function
> does.
>
Per the discussion, I think put_prev_task_balance() might be an
appropriate one.

Thanks,
Chenyu
> -- Steve
> 
> >  
> >  	for_each_class(class) {
> >  		p = class->pick_next_task(rq);
>