linux-kernel - Re: false nr_running check in load balance?

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Message-ID: <20130813073842.GP27162@twins.programming.kicks-ass.net>
Date:	Tue, 13 Aug 2013 09:38:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lei Wen <adrian.wenl@...il.com>
Cc:	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, leiwen@...vell.com
Subject: Re: false nr_running check in load balance?

On Tue, Aug 13, 2013 at 12:45:12PM +0800, Lei Wen wrote:
> > Not quite right; I think you need busiest->cfs.h_nr_running.
> > cfs.nr_running is the number of entries running in this 'group'. If
> > you've got nested groups like:
> >
> >  'root'
> >    \
> >    'A'
> >    / \
> >   t1 t2
> >
> > root.nr_running := 1 'A', even though you've got multiple running tasks.
> >
> 
> You're absolutely right for this. :)
> I miss it for not considering the group case...
> 
> Then do you think it is necessary to do below change in load_balance() code?
>  -       if (busiest->nr_running > 1) {
>  +       if (busiest->cfs.h_nr_running > 1) {
> 

Yes I think that would be fine.
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