linux-kernel - Re: [PATCH v4 5/5] sched: add two functions for att(det)aching a task to(from) a cfs

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Date:	Tue, 1 Sep 2015 11:59:03 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, yuyang.du@...el.com
Subject: Re: [PATCH v4 5/5] sched: add two functions for att(det)aching a
 task to(from) a cfs_rq

On Tue, Sep 01, 2015 at 09:28:49AM +0900, Byungchul Park wrote:
> On Mon, Aug 31, 2015 at 05:21:38PM +0200, Peter Zijlstra wrote:
> > On Thu, Aug 20, 2015 at 08:35:16PM +0900, Byungchul Park wrote:
> > > On Thu, Aug 20, 2015 at 08:22:00PM +0900, byungchul.park@....com wrote:
> > 
> > > > +	/*
> > > > +	 * If it's !queued, then only when the task is sleeping it has a
> > > > +	 * non-normalized vruntime, that is, when the task is being migrated
> > > > +	 * it has a normailized vruntime.
> > > > +	 */
> > > 
> > > i tried to change your XXX comment. i think it can be explaned like this.
> > > don't you think so? i want to hear any opinions about this.
> > > 
> > > > +	if (p->state == TASK_RUNNING)
> > > > +		return true;
> > 
> > 
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7943,11 +7943,10 @@ static inline bool vruntime_normalized(s
> >  		return true;
> >  
> >  	/*
> > -	 * If it's !queued, then only when the task is sleeping it has a
> > -	 * non-normalized vruntime, that is, when the task is being migrated
> > -	 * it has a normalized vruntime.
> > +	 * If it's !queued, sleeping tasks have a normalized vruntime,
> > +	 * see dequeue_entity().
> 
> check the condition "!(flags & DEQUEUE_SLEEP)" for doing normalizing in
> dequeue_entity(). i think you have to keep my original comment, or
> modify your comment to something like below.
> 
> before - If it's !queued, sleeping tasks have a normalized vruntime,
> after - If it's !queued, sleeping tasks have a non-normalize vruntime,
> 
> but.. i think it would be better that you keep my original comment..

i mean "it would be better that you leave my original comment unchanged".

> 
> >  	 */
> > -	if (p->state == TASK_RUNNING)
> > +	if (!p->se.on_rq)
> >  		return true;
> >  
> >  	return false;
> > 
> > 
> > Does that make sense?
> > 
> > I think using p->state for this is fragile, as we could be racy with any
> > random blocking primitive that does set_current_state() _before_
> > actually calling into the scheduler.
> > 
> > 
> > --
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