Re: S0iX Ultra Low Power States

[Dennis Wassenberg <dennis.wassenberg@secunet.com>]

Hi Kristen,

Now I am investigating on an other device (Microsoft Surface Pro 3).
There I followed your instructions but without success. Even powertop
assumes that everything is tuned for low power.

This device takes 2.5 Watt in freeze mode. So I assume that the S0i3
state was not entered automatically. Is there any possibility to check
which precondition is not satisfied? Or can I force the system to enter
S0iX states?

Thank you & best regards,
Dennis

On 27.11.2014 12:50, Dennis Wassenberg wrote:
> Hi Kristen,
> 
> thank you for these hints. Especially these regarding PCIe endpoint
> devices. I found that some of these was configured to be always on which
> prevents the system from entering the S0iX states. After changing this
> the power consumption reduced to approximately 0.5 Watt.
> 
> Thank you & best regards,
> 
> Dennis
> 
> On 25.11.2014 19:13, Kristen Carlson Accardi wrote:
>> On Tue, 25 Nov 2014 13:51:37 +0100
>> Dennis Wassenberg <dennis.wassenberg@secunet.com> wrote:
>>
>>> Hi,
>>>
>>> I would like to know more about the Linux power management in
>>> correlation to the Intel S0iX Ultra Low Power States.
>>>
>>> Systems which have a Windows 8 Logo must support Connected Standby (or
>>> InstantGo, however it is called). One of the requirements getting this
>>> logo is that the ACPI firmware must not provide an S3 object in the root
>>> of the namespace. This means that Linux can not use the S3 mode.
>>>
>>> To archive a very low power consumption Microsoft uses the Ultra Low
>>> Power States S0i1 and S0i3. Is there a way to use these low power states
>>> in linux for Haswell/LynxPoint or Broadwell/Skylake platforms?
>>>
>>> I read something about these states. Such that they can be activated
>>> automatically but there are some preconditions (e.g. certain IO devices
>>> have to put into a low power state, graphics off, only one CPU online,
>>> ...). If I enter the S1 Low Power State (with additional
>>> disable_nonboot_cpus) all of these preconditions should be fulfilled?!
>>> But I can not observe that the there is a power consumption less than 1
>>> Watt.
>>>
>>> Thank you & Best regards,
>>>
>>> Dennis
>>
>> Hi,
>> On haswell ULT and Broadwell ULT these states can be entered as part of
>> Linux's normal Idle flow if some preconditions are met.  You should run
>> powertop to ensure that all devices are tuned for low power.  The
>> embedded display must be off. (no external display connected).  You
>> should confirm that all PCIe endpoint devices on your platform support
>> ASPM and L1 substates (using lspci).  If they do not, you must ensure
>> they are in D3.  You should kill or freeze any processes that frequently
>> wake in order to improve your average battery life.  You can use
>> powertop or turbostat to confirm entry into pc8/pc9/pc10.
>>
>> Good luck.
>> Kristen
>>
>>
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