linux-kernel - Re: [PATCH 8/8] intel_idle: create a native cpuidle driver for select intel processors

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Date:	Fri, 28 May 2010 13:43:35 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	x86@...nel.org, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 8/8] intel_idle: create a native cpuidle driver for select
 intel processors

On Fri, 28 May 2010, Chase Douglas wrote:

> On Fri, 2010-05-28 at 00:16 -0400, Len Brown wrote:
> > > I see that you have updated this code in your tree to disable C4 and C6
> > > on atom. This has piqued my curiosity. I've now seen 2 atom netbooks
> > > from different OEMs that hide C4 when you plug the power in. After the
> > > first machine I thought, "must be a BIOS/ACPI bug," but now I'm
> > > beginning to wonder if there's some issue with atom C4 states? That's
> > > beside the fact that I've not seen C6 on either machine at all. Do you
> > > have any insight?
> > 
> > The reasoning behind ACPI taking deep C-states away
> > when on AC is the assumption that users on AC
> > care more about low latency and high performance
> > than they care about power savings, heat, and noise.
> 
> Maybe they forgot that a netbook is still a *lap*top when they did this,
> cause I can't keep mine on my lap when it's plugged in :). The CPU idles
> at 60 centigrade when powered on, and drops to a manageable 30-ish
> centigrade when running on battery.
> 
> > So my intent is to give Linux control over this decision,
> > via PM_QOS or otherwise.  At the moment C4 is commented out
> > because when i first tested it failed the lapic timer workaround.
> 
> I am looking forward to testing out these changes on my netbook once
> this issue get sorted out!

Atom C4 works in the current driver in the git tree -- test it now!

cheers,
-Len

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