Date: Wed, 20 Oct 2004 21:59:30 +0200
From: Ingo Molnar <mingo@elte.hu>
To: John Hawkes <hawkes@oss.sgi.com>
Cc: nickpiggin@yahoo.com.au, akpm@osdl.org, linux-kernel@vger.kernel.org,
       jbarnes@sgi.com, hawkes@sgi.com
Subject: Re: [PATCH, 2.6.9] improved load_balance() tolerance for pinned tasks
Message-ID: <20041020195930.GA29735@elte.hu>
References: <200410201936.i9KJa4FF026174@oss.sgi.com>
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* John Hawkes <hawkes@oss.sgi.com> wrote:

> A large number of processes that are pinned to a single CPU results in
> every other CPU's load_balance() seeing this overloaded CPU as "busiest",
> yet move_tasks() never finds a task to pull-migrate.  This condition
> occurs during module unload, but can also occur as a denial-of-service
> using sys_sched_setaffinity().  Several hundred CPUs performing this
> fruitless load_balance() will livelock on the busiest CPU's runqueue
> lock.  A smaller number of CPUs will livelock if the pinned task count
> gets high.  This simple patch remedies the more common first problem:
> after a move_tasks() failure to migrate anything, the balance_interval
> increments.  Using a simple increment, vs.  the more dramatic doubling of
> the balance_interval, is conservative and yet also effective.
> 
> John Hawkes
> 
> 
> Signed-off-by: John Hawkes <hawkes@sgi.com>

looks good to me.

Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo
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