Massive power regression going 3.4->3.5

[James Bottomley]

On Mon, 2012-07-30 at 11:23 -0700, Keith Packard wrote:
> James Bottomley <James.Bottomley at HansenPartnership.com> writes:
> 
> > On Mon, 2012-07-30 at 09:33 -0700, Keith Packard wrote:
> >> James Bottomley <James.Bottomley at HansenPartnership.com> writes:
> >> 
> >> > OK, I've run the bisect as far as I can.  It looks to be in the drm
> >> > tree.  Unfortunately, this tree has several merge points, some of which
> >> > go further back than v3.4.  Unfortunately, once the bisect steps back
> >> > before 3.4, we lose the changes that gave us the power savings, making
> >> > further debugging impossible
> >> 
> >> What machine is this on? There are a few 'disable some power savings'
> >> patches in that list to work around issues on various machines; knowing
> >> what machine you're using can isolate which ones might have had some
> >> effect on power usage...
> >
> > Lenovo X220i
> 
> I don't see a whole lot of context from the elided email bits you'd sent
> previously; can you summarize the issue in terms of how much power
> savings you're losing, how you're measuring it and what's going on in
> the system when the power savings is different?

Sure.  Going from 3.3->3.4 we saw massive increase in power savings due
to various autosuspend updates.  The idle power consumption of the X220i
went from about 13W to 6.5W.  In 3.5 this seems to be reversed, with the
idle power consumption back up to around 14W.  I can't quite believe the
graphics chip is responsible for around 7W, so it looks like it's some
interaction between graphics and other subsystems.

> Have you tried measuring power with X not running? How about with
> compositing and other desktop effects disabled? 

Sure, I can try doing that ... but remember this is a system where the
drm is used for the console as well.

James