Re: [PATCH] Add idle power save for ppc 4xx

[Michael Ellerman <michael@ellerman.id.au>]

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On Mon, 2008-03-31 at 13:19 -0500, Jerone Young wrote:
> On Mon, 2008-03-31 at 13:05 -0500, Josh Boyer wrote:
> > On Mon, 31 Mar 2008 12:07:17 -0500
> > Josh Boyer <jwboyer@gmail.com> wrote:
> > 
> > > On Mon, 2008-03-31 at 08:12 -0500, Jerone Young wrote:
> > > > # HG changeset patch
> > > > # User Jerone Young <jyoung5@us.ibm.com>
> > > > # Date 1206969060 18000
> > > > # Node ID 10aea37177130bbe5de7bee6ec06d9010bc5da1f
> > > > # Parent  1506aa38ddabb0bf73fff3ac3f3db5f9ef6458cc
> > > > Add idle power save for ppc 4xx
> > > > 
> > > > This patch sets the wait state MSR when power_save is called in cpu_idle loop for ppc4xx. This is mainly to help out virtualization solutions such as KVM. This way the virtualization soultions are able to tell if the guest kernel is idle.
> > > > 
> > > > I have tested this on hardware & KVM virtual guest.
> > > 
> > > I'm not overly thrilled with adding this to all of 4xx.  It doesn't
> > > actually save much power at all (1% on a project that actually measured
> > > it with an amp meter recently) and there's really no other benefit to
> > > doing it outside of the virtual guest case.
> > > 
> > > I'm assuming you pass a dtb to the virtual guest when you start it up.
> > > Could you define a property in the CPU node there that can be parsed to
> > > use the power_save function instead of always making it the default?
> > 
> > Actually, you probably don't want this as a property in the device
> > tree.  It doesn't describe hardware.  A Kconfig option might be
> > warranted though.
> 
> I'll go with the Kconfig option. 

Go with a device-tree check. The pseries kernel supports both bare-metal
and hypervisor in the same kernel image, and it works out which it's
running on by looking at the device-tree. This seems equivalent to me?

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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