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

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Date:	Mon, 11 Jun 2007 23:12:48 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	Tejun Heo <htejun@...il.com>,
	Kristen Carlson Accardi <kristen.c.accardi@...el.com>,
	james.bottomley@...eleye.com, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/3] AHCI Link Power Management

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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