linux-kernel - Re: apm system does not power off anymore

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Message-Id: <20071014234149.39a4f08a.akpm@linux-foundation.org>
Date:	Sun, 14 Oct 2007 23:41:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Stephen Rothwell <sfr@...b.auug.org.au>
Cc:	Olaf Hering <olaf@...fle.de>, linux-kernel@...r.kernel.org
Subject: Re: apm system does not power off anymore

On Mon, 15 Oct 2007 16:37:20 +1000 Stephen Rothwell <sfr@...b.auug.org.au> wrote:

> On Sun, 14 Oct 2007 23:23:16 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > Also, it's bad that the operator has to provide some special boot command-line
> > option to make the machine work properly.  Please consider this to be a
> > bug.  Has it always needed apm=power-off?
> 
> It has always been that way because the behaviour of APM on SMP is not
> defined.  We discovered early that it will work (at least for powering
> off) for most SMP machines as long as the APM calls are done on CPU 0.
> However on an SMP machine that does not cope, very bad things happen -
> thus the operator has to explictly enable the power off behaviour on an
> SMP box.  (On UP power off is enabled by default.)

hrm, OK.

But it could have been controlled by a more-user-friendly runtime knob, I
guess.  Not that it's worth changing that now.

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