Re: [PATCH]AC/DC notifier

["Tippett, Matthew" <matthew.tippett@amd.com>]

(Resending as text-only - sorry)

Bringing this item back up again.

I am not suggesting that the application of any particular policy 
appears within the kernel or userspace or a secondary policy engine.   
In general I am also against codifying policy within drivers.

I am interested seeing the ACPI notifier mechanism expanded to allow 
AC/DC state changes propagate to other kernel drivers without requiring 
a userspace in between.

I can continue to come up with real scenarios that would possibly 
require kernel-to-kernel notification, but would rather focus this 
discussion of the pure technical issues associated with adding the 
notifier to the AC/DC ACPI subsystem. 

Remember it is a one line patch.

Regards,

Matthew

-------- Original Message  --------
Subject: Re: [PATCH][ACPI] AC/DC notifier
From: Willy Tarreau <w@1wt.eu>
To: Pavel Machek <pavel@ucw.cz>
Cc: "Matthew Garrett" <mjg59@srcf.ucam.org>, "Tippett, Matthew" 
<Matthew.Tippett@amd.com>, "Langsdorf, Mark" <mark.langsdorf@amd.com>, 
lenb@kernel.org, linux-acpi@vger.kernel.org, 
linux-kernel@vger.kernel.org, "Li, Samuel" <Samuel.Li@amd.com>
Date: 08/16/2009 03:40 AM
>
> On Fri, Aug 14, 2009 at 06:32:33PM +0200, Pavel Machek wrote:
> > On Wed 2009-08-12 01:55:32, Matthew Garrett wrote:
> > > On Tue, Aug 11, 2009 at 08:51:49PM -0400, Tippett, Matthew wrote:
> > >
> > > >    From a graphics perspective (your area of expertise), this 
> will allow KMS
> > > >    drivers to do some more intelligent actions based on the 
> ac/dc state.
> > > >    Some examples of this could be improving the power 
> consumption of the
> > > >    graphics hardware through adapting clock memory/engine 
> settings for
> > > >    reduced power consumption, reducing refresh rate of the 
> display to reduce
> > > >    scanout memory access, adjusting backlight brightness, etc.
> > >
> > > Right. As you say, my concern is that most of this should belong in
> > > userspace. Where we risk hardware damage there's an obvious 
> argument for
> > > doing this in kernel, but we should ensure that that's limited to
> > > whatever coarse-grain handling is absolutely required rather than 
> doing
> > > things like touching display brightness.
> >
> > Yep... Some may want to save power even when AC is online -- like when
> > running on UPS. Some may want max performmance even on battery.
>
> Wholeheartly agreed. IMHO, there's absolutely no relation between power
> source and the expected performance. It's really frustrating when your
> laptop becomes a snail on battery, as well as it's annoying to hear it
> sound like a hairdryer when plugged to mains. This should only be the
> user's choice. Mine automatically adjusts its frequency on demand,
> regardless of the power source, which provides me with the best
> experience. I think that all the tricks used to save power when running
> on battery were invented by laptop makers to artificially show longer
> lasting eventhough the machine sometimes becomes barely usable. For
> instance, some of them dim the backlight so that you can't read anything
> in full light, so you need a power prolongator to use them outside !
>
> Also, with the new trend of laptops making use of huge power-hungry 3D
> graphic chips which suck all the juice out of your battery in less than
> two hours doing nothing, you'd better run at full speed when on battery
> to save energy for CPU-bound tasks, because eventhough the CPU eats more
> power, you significantly reduce the run time, thus the static consumption
> (GPU, backlight, hard disk, ...).
>
> Willy
>
>