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

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Message-ID: <466E0F28.3040701@linux.intel.com>
Date:	Mon, 11 Jun 2007 20:12:40 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Jeff Garzik <jeff@...zik.org>
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

Jeff Garzik wrote:
> 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.
> 
yes I'm not arguing against that. I was trying to find out (and 
suggest-unless-proven-otherwise) that the 2 are not exclusive or 
conflicting... in fact I assume both are wanted concurrently.
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