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Old 12-06-2011, 12:25 PM
Colin Ian King
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

Hi there,

Aggressive Link Power Management (ALPM) is a mechanism where a SATA AHCI
controller can put the SATA link that connects to the disk into a very
low power mode during periods of zero I/O activity and into an active
power state when work needs to be done. Tests show that this can save
around 0.5-1.5 Watts of power on a typical system.


ALPM is now available in several SATA controllers that use the Advanced
Host Controller Interface (AHCI). However, there is some anecdotal
evidence that some controllers may go into a low power state incorrectly
and this ends up causing data loss. Ubuntu has the ability to use ALPM
but it it disabled by default since it can cause data loss on some
machines.


We are looking for (brave?) volunteers to test ALPM for 2 reasons:

1) help to identify typical power savings on a range of machines
2) help to identify chipsets (and machines) where ALPM works reliably
and also where it is broken and needs fixing.


An ALPM crowd-sourcing testing Wiki page has been created that describes
a testing methodology and has a table for test results:
https://wiki.ubuntu.com/Kernel/PowerManagementALPM


Please note that there is a possibility that ALPM MAY CAUSE DATA LOSS on
some machines, so please ensure you have backed up your data or don't
mind the risk in losing your data.


Colin

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Old 12-06-2011, 04:14 PM
Tim Gardner
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On 12/06/2011 06:25 AM, Colin Ian King wrote:

Hi there,

Aggressive Link Power Management (ALPM) is a mechanism where a SATA AHCI
controller can put the SATA link that connects to the disk into a very
low power mode during periods of zero I/O activity and into an active
power state when work needs to be done. Tests show that this can save
around 0.5-1.5 Watts of power on a typical system.

ALPM is now available in several SATA controllers that use the Advanced
Host Controller Interface (AHCI). However, there is some anecdotal
evidence that some controllers may go into a low power state incorrectly
and this ends up causing data loss. Ubuntu has the ability to use ALPM
but it it disabled by default since it can cause data loss on some
machines.

We are looking for (brave?) volunteers to test ALPM for 2 reasons:

1) help to identify typical power savings on a range of machines
2) help to identify chipsets (and machines) where ALPM works reliably
and also where it is broken and needs fixing.

An ALPM crowd-sourcing testing Wiki page has been created that describes
a testing methodology and has a table for test results:
https://wiki.ubuntu.com/Kernel/PowerManagementALPM

Please note that there is a possibility that ALPM MAY CAUSE DATA LOSS on
some machines, so please ensure you have backed up your data or don't
mind the risk in losing your data.

Colin



How about screen backlight management? I've noticed that my screen at
full brightness consumes about 4W compared to screen off. Should we at
least be measuring that ?


--
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Old 12-06-2011, 04:15 PM
Colin Ian King
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On 06/12/11 17:14, Tim Gardner wrote:

On 12/06/2011 06:25 AM, Colin Ian King wrote:

Hi there,

Aggressive Link Power Management (ALPM) is a mechanism where a SATA AHCI
controller can put the SATA link that connects to the disk into a very
low power mode during periods of zero I/O activity and into an active
power state when work needs to be done. Tests show that this can save
around 0.5-1.5 Watts of power on a typical system.

ALPM is now available in several SATA controllers that use the Advanced
Host Controller Interface (AHCI). However, there is some anecdotal
evidence that some controllers may go into a low power state incorrectly
and this ends up causing data loss. Ubuntu has the ability to use ALPM
but it it disabled by default since it can cause data loss on some
machines.

We are looking for (brave?) volunteers to test ALPM for 2 reasons:

1) help to identify typical power savings on a range of machines
2) help to identify chipsets (and machines) where ALPM works reliably
and also where it is broken and needs fixing.

An ALPM crowd-sourcing testing Wiki page has been created that describes
a testing methodology and has a table for test results:
https://wiki.ubuntu.com/Kernel/PowerManagementALPM

Please note that there is a possibility that ALPM MAY CAUSE DATA LOSS on
some machines, so please ensure you have backed up your data or don't
mind the risk in losing your data.

Colin



How about screen backlight management? I've noticed that my screen at
full brightness consumes about 4W compared to screen off. Should we at
least be measuring that ?



It's on my very long list of things to measure


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Old 12-06-2011, 07:44 PM
Colin Ian King
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On 06/12/11 17:14, Tim Gardner wrote:

On 12/06/2011 06:25 AM, Colin Ian King wrote:

Hi there,

Aggressive Link Power Management (ALPM) is a mechanism where a SATA AHCI
controller can put the SATA link that connects to the disk into a very
low power mode during periods of zero I/O activity and into an active
power state when work needs to be done. Tests show that this can save
around 0.5-1.5 Watts of power on a typical system.

ALPM is now available in several SATA controllers that use the Advanced
Host Controller Interface (AHCI). However, there is some anecdotal
evidence that some controllers may go into a low power state incorrectly
and this ends up causing data loss. Ubuntu has the ability to use ALPM
but it it disabled by default since it can cause data loss on some
machines.

We are looking for (brave?) volunteers to test ALPM for 2 reasons:

1) help to identify typical power savings on a range of machines
2) help to identify chipsets (and machines) where ALPM works reliably
and also where it is broken and needs fixing.

An ALPM crowd-sourcing testing Wiki page has been created that describes
a testing methodology and has a table for test results:
https://wiki.ubuntu.com/Kernel/PowerManagementALPM

Please note that there is a possibility that ALPM MAY CAUSE DATA LOSS on
some machines, so please ensure you have backed up your data or don't
mind the risk in losing your data.

Colin



How about screen backlight management? I've noticed that my screen at
full brightness consumes about 4W compared to screen off. Should we at
least be measuring that ?



Tim,

measuring this is fairly easy but I'm not sure what you'd like tested.
Backlights are adjusted on AC or battery automatically and users can
tweak these using hotkeys too. So, do we want to accurately know just
how much power

we consume, with different levels?

I suspect I should also investigate something that lesswatts.org reports:

"Interestingly, in our measurements we have found that, at least on
newer laptops, the kernel sysfs method (which tends to use the BIOS on
the machine) seems to not control the actual backlight, but rather
change the colors of the pixels on the screen to appear darker. Using
darker pixels obviously doesn't save as much power as reducing the
intensity of the backlight."


..so that I will at least poke at that.

The backlight issue makes me also think about other non-obvious
settings. For example, with framebuffer compression we use less power to
clock out the image, so I'd like to measure a default desktop background
vs a plain background vs a complex background image.


And also I will be investigating the white vs black pixels setting when
the screen is blanked - apparently white saves power.


If any one has any further ideas, let me know.

Colin

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Old 12-06-2011, 07:58 PM
Tim Gardner
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On 12/06/2011 01:44 PM, Colin Ian King wrote:

On 06/12/11 17:14, Tim Gardner wrote:

On 12/06/2011 06:25 AM, Colin Ian King wrote:


<snip>



How about screen backlight management? I've noticed that my screen at
full brightness consumes about 4W compared to screen off. Should we at
least be measuring that ?


Tim,

measuring this is fairly easy but I'm not sure what you'd like tested.
Backlights are adjusted on AC or battery automatically and users can
tweak these using hotkeys too. So, do we want to accurately know just
how much power
we consume, with different levels?



Knowing what the backlight is consuming at various levels gives you
quantitative input to your screen blanking interval decision. I find it
quite annoying to have my screen go blank after 3 minutes (the default),
so if I _knew_ what it was costing me in terms of battery time, then I
could adjust that blanking interval accordingly.



I suspect I should also investigate something that lesswatts.org reports:

"Interestingly, in our measurements we have found that, at least on
newer laptops, the kernel sysfs method (which tends to use the BIOS on
the machine) seems to not control the actual backlight, but rather
change the colors of the pixels on the screen to appear darker. Using
darker pixels obviously doesn't save as much power as reducing the
intensity of the backlight."

..so that I will at least poke at that.

The backlight issue makes me also think about other non-obvious
settings. For example, with framebuffer compression we use less power to
clock out the image, so I'd like to measure a default desktop background
vs a plain background vs a complex background image.

And also I will be investigating the white vs black pixels setting when
the screen is blanked - apparently white saves power.



Yeah, it would be nice to know what models take this route as I suspect
it'll have an adverse impact on power consumption.



If any one has any further ideas, let me know.

Colin



--
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Old 12-06-2011, 07:59 PM
Seth Forshee
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On Tue, Dec 06, 2011 at 08:44:30PM +0000, Colin Ian King wrote:
> And also I will be investigating the white vs black pixels setting
> when the screen is blanked - apparently white saves power.

Why don't we just dispense with the blanking and power off the display
and the backlight altogether?

Seth

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Old 12-07-2011, 10:01 AM
Andy Whitcroft
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On Tue, Dec 06, 2011 at 02:59:23PM -0600, Seth Forshee wrote:
> On Tue, Dec 06, 2011 at 08:44:30PM +0000, Colin Ian King wrote:
> > And also I will be investigating the white vs black pixels setting
> > when the screen is blanked - apparently white saves power.
>
> Why don't we just dispense with the blanking and power off the display
> and the backlight altogether?

I think we are leary of turning the thing off as at least in the old
days there was a desire to not turn them on and off all the time,
probabally as there was a discharge tube in the mix. Perhaps that is
true for some external monitors but likely for a panel they are LED lit
now.

-apw

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Old 12-18-2011, 09:07 AM
Amit Kucheria
 
Default SATA Aggressive Link Power Management (ALPM) - call for testing

On 11 Dec 06, Colin King wrote:
>
> The backlight issue makes me also think about other non-obvious
> settings. For example, with framebuffer compression we use less
> power to clock out the image, so I'd like to measure a default
> desktop background vs a plain background vs a complex background
> image.
>
> And also I will be investigating the white vs black pixels setting
> when the screen is blanked - apparently white saves power.

Are laptops seeing OLED/AMOLED displays like phones these days? If so, white
backgrounds will kill battery life.

> If any one has any further ideas, let me know.

Is Bluetooth on your list of things to silence? It might save a watt by
default.

There are some other experimental techniques around sched_mc and hotplug that
are being used by ARM vendors but might not be suitable for a LTS release.

/Amit

--
--------------------------------------------------------------------------------
Amit Kucheria, Power Management Tech Lead, Linaro || amit.kucheria@canonical.com
--------------------------------------------------------------------------------

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