linux-kernel - Re: [OLPC-devel] Re: [RFC][PATCH 1/2] ACPI: Idle Processor PM Improvements

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Date:	Thu, 31 Aug 2006 23:53:04 -0400
From:	Len Brown <len.brown@...el.com>
To:	jg@...top.org
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	ACPI ML <linux-acpi@...r.kernel.org>,
	Adam Belay <abelay@...ell.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>, devel@...top.org
Subject: Re: [OLPC-devel] Re: [RFC][PATCH 1/2] ACPI: Idle Processor PM Improvements

On Thursday 31 August 2006 20:30, Jim Gettys wrote:
> On Thu, 2006-08-31 at 17:13 -0600, Bjorn Helgaas wrote:
> > On Wednesday 30 August 2006 13:43, Matthew Garrett wrote:
> > > That would be helpful. For the One Laptop Per Child project (or whatever 
> > > it's called today), it would be advantageous to run without acpi.
> > 
> > Out of curiosity, what is the motivation for running without acpi?
> > It costs a lot to diverge from the mainstream in areas like that,
> > so there must be a big payoff.  But maybe if OLPC depends on acpi
> > being smarter about power or code size or whatever, those improvements
> > could be made and everybody would benefit.
> 
> Good question; I see Matthew beat me to part of the explanation, but
> here is more detail:

I recommended that the OLPC guys not use ACPI.

I do not think it would benefit their system.  Although it is an i386
instruction set, their system is more like an embedded device than
like a traditional laptop.

The Geode doesn't suport any C-states -- so ACPI wouldn't help them there anyway.

As Jim wrote, OLPC plans to suspend-to-ram from idle, and to keep video running,
so ACPI wouldn't help them on that either.

Re: optimizing suspend/resume speed
I expect suspend/resume speed has more to do with devices than with ACPI.
But frankly, with gaping functionality holes in Linux suspend/resume support such as
IDE and SATA, I think that optimizing for suspend/resume speed on a mainstream laptop
is somewhat "forward looking".

-Len
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