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

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Date:	Thu, 27 May 2010 21:44:16 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Thomas Renninger <trenn@...e.de>
Cc:	linux-pm@...ts.linux-foundation.org, x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	sfr@...b.auug.org.au
Subject: Re: [linux-pm] [PATCH 8/8] intel_idle: create a native cpuidle driver
 for select intel processors

On Thu, 27 May 2010, Thomas Renninger wrote:

> On Thursday 27 May 2010 04:42:31 Len Brown wrote:
> > From: Len Brown <len.brown@...el.com>
> ... 
> > CONFIG_INTEL_IDLE=m is not recommended unless the system
> > has a method to guarantee intel_idle loads before ACPI's
> > processor_idle.

> Then it should better be declared bool instead of tristate until it
> works.

intel_idle as a module works fine, and tristate should be retained.

If user-space chooses to load intel_idle before acpi processor,
then it correctly handlees idle states and acpi
correctly yields.  If user space gets them in the other order,
then user-space gets what it asked for.

The fact that a typical desktop distro load acpi-cpufreq first,
and that depends on the acpi processor driver should not prohibit
intel_idle from being modular.

Indeed, intel_idle has every right to be moduler on a system
where CONFIG_ACPI=n...

> > This driver does not yet know about cpu online/offline
> > and thus will not yet play well with cpu-hotplug.

> What means does not play well yet, suspend or manually offlining a core 
> will eventually (for sure?) hang the machine?

It means less power savings savings than optimal
for processors not present at module load time.

> If this is known broken, should this already be spread through
> linux-next?

If you know somebody with a system that supports CPU hot-add
on one of the processors supported by intel_idle, and they
are willing to test linux-next, please have them contact me.

thanks,
-Len Brown, Intel Open Source Technology Center
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