Re: [patch 0/3] AHCI Link Power Management

[Jeff Garzik <jeff@garzik.org>]

Arjan van de Ven wrote:
> Tejun Heo wrote:
> > Kristen Carlson Accardi wrote:
> > > Hi,
> > > This series of patches enables Aggressive Link Power Management for 
> > > AHCI devices, as documented in the AHCI spec.  On my laptop (a Lenovo 
> > > X60), this
> > > saves me a full watt of power.  On other systems, reported power savings
> > > range from .5-1.5 Watts.  It has been tested by the kind folks at 
> > > #powertop
> > > with similar results.  Please give it a try and let me know what you 
> > > think.
> >
> > I'm not sure about this.  We need better PM framework to support
> > powersaving in other controllers and some ahcis don't save much when
> > only link power management is used, 
>
> do you have data to support this? The data we have from this patch is 
> that it saves typically a Watt of power (depends on the machine of 
> course, but the range is 0.5W to 1.5W). If you want to also have an even 
> more agressive thing where you want to start disabling the entire 
> controller... I don't see how this is in conflict with saving power on 
> the link level by "just" enabling a hardware feature ....

SATA standard defines lower power phy states.  So the same argument 
you're using for AHCI applies there too -- "just" enabling an existing 
hardware feature.

	Jeff


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