Date: Thu, 27 Sep 2007 09:56:38 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Mike Galbraith <efault@gmx.de>,
       linux-kernel@vger.kernel.org
Subject: Re: [git] CFS-devel, latest code
Message-ID: <20070927075638.GA13963@elte.hu>
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* Dmitry Adamushko <dmitry.adamushko@gmail.com> wrote:

> humm... I think, it'd be safer to have something like the following 
> change in place.
> 
> The thing is that __pick_next_entity() must never be called when 
> first_fair(cfs_rq) == NULL. It wouldn't be a problem, should 
> 'run_node' be the very first field of 'struct sched_entity' (and it's 
> the second).
> 
> The 'nr_running != 0' check is _not_ enough, due to the fact that 
> 'current' is not within the tree. Generic paths are ok (e.g. 
> schedule() as put_prev_task() is called previously)... I'm more 
> worried about e.g. migration_call() -> CPU_DEAD_FROZEN -> 
> migrate_dead_tasks()... if 'current' == rq->idle, no problems.. if 
> it's one of the SCHED_NORMAL tasks (or imagine, some other use-cases 
> in the future -- i.e. we should not make outer world dependent on 
> internal details of sched_fair class) -- it may be "Houston, we've got 
> a problem" case.
> 
> it's +16 bytes to the ".text". Another variant is to make 'run_node' 
> the first data member of 'struct sched_entity' but an additional check 
> (se ! = NULL) is still needed in pick_next_entity().

looks good to me - and we already have something similar in sched_rt.c. 
I've added your patch to the queue. (Can i add your SoB line too?)

	Ingo
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