Massive power regression going 3.4->3.5

[James Bottomley]

On Tue, 2012-07-31 at 08:31 +0100, James Bottomley wrote:
> 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.

Actually, bad news: it looks like the problem is drm:

on 3.5 killing X causes idle power to go 14W -> 5.9W
on 3.4.6 killing X causes idle power to go 6.8W -> 5.7W

James