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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Message-ID: <20150901002849.GA30881@byungchulpark-X58A-UD3R>
Date:	Tue, 1 Sep 2015 09:28:49 +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 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..

>  	 */
> -	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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