Massive power regression going 3.4->3.5

James Bottomley James.Bottomley at
Tue Jul 31 08:09:44 PDT 2012

On Tue, 2012-07-31 at 07:27 -0700, Keith Packard wrote:
> James Bottomley <James.Bottomley at> writes:
> > 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
> That's actually pretty good news -- you're just not getting to RC6
> when X is running, but RC6 is otherwise working. And, yes, the GPU
> really can suck that much power. The debug info that Chris pointed you
> at should tell a more complete story. For comparison, on my sandybridge
> box this morning:

Well, I don't know what it means, but I have a culprit from bisect (I
managed to manually verify the bisection heads which would step back
into 3.3).

2911a35b2e4eb87ec48d03aeb11f019e51ae3c0d is the first bad commit
commit 2911a35b2e4eb87ec48d03aeb11f019e51ae3c0d
Author: Ben Widawsky <ben at>
Date:   Thu Apr 5 14:47:36 2012 -0700

    drm/i915: use semaphores for the display plane

I'm going to try building 3.5 with this reverted (it doesn't revert


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